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PERFORMANCE EVALUATION AND CROSS-CALIBRATION OF 
®
CAPINTEC  CRC 15R AND COMECER DOSE CALIBRATORS 
 
Presented to 
 
DEPARTMENT OF MEDICAL PHYSICS 
SCHOOL OF NUCLEAR AND ALLIED SCIENCES 
UNIVERSITY OF GHANA 
BY 
ELIAS MWAPE 
(10611916) 
 
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE AWARD OF 
A 
MASTER OF PHILOSOPHY 
IN 
MEDICAL PHYSICS 
 
JULY, 2018
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DECLARATION  
This thesis is the result of research work undertaken by Mr. ELIAS MWAPE in the 
Department of Medical Physics, School of Nuclear and Allied Sciences, University 
of Ghana, under the supervision of Prof. A.K Kyere, Dr. F. Hasford and Dr. E.K. 
Sosu. 
Sign………………………………          Date……………………………  
Elias Mwape 
(Student)  
Supervisor’s Declaration  
The preparation and presentation of this thesis were supervised in accordance with 
guidelines on supervision of thesis laid down by the University of Ghana.  
Sign……………………………               Date……………………………  
 Dr. F. Hasford  
 (Principal supervisor) 
 
Sign……………………………               Date……………………………  
 Prof. A.K Kyere 
(Co-supervisor) 
 
Sign……………………………               Date……………………………  
Dr. E.K .Sosu 
(Co-supervisor) 
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DEDICATION 
This research work is dedicated to my lovely fiancée Violet Mbwili for the love, 
moral and spiritual support. It is also dedicated to my parents Brendah Kasali and 
Everisto Mwape for making me see the value of education. Last but not the least, 
dedicated also to all my friends and family especially Bishop Justine Gondwe and the 
Macedonia church family.   
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ACKNOWLEDGEMENTS 
First and foremost I give Glory, honor and adoration to God Almighty for His grace, 
guidance and protection throughout the course of this research study. Indeed he has 
being my strength and shield. 
I am also forever indebted to the dedicated team of supervisors Professor A.W.K. 
Kyere, Dr. Francis Hasford and Dr. Edem Sosu for their invaluable guidance and 
support rendered to me in seeing this research work to completion.  
Special thanks goes to my sponsor, IAEA for the financial support without which 
this work could not have come to a successful end. 
I would also like to thank all my lecturers from the Graduate School of Nuclear and 
Allied Sciences (SNAS) for the coursework which gave me better foundation for 
understanding this research work. 
I am also grateful to the nuclear medicine department at Korle-Bu Teaching Hospital 
for allowing to me to use the equipment and materials in the Department. Special 
thanks more especially to the nuclear medicine technologists Mr. Daniel Ashley and 
Mr. Adu Asimeng Sarkodie for their cooperation and support throughout the process 
of data collection.  
Special thanks to the entire Nuclear medicine unit at the University Teaching 
Hospital in Zambia for the encouragement and support throughout my stay in Ghana. 
Finally, special thanks to my friends Clement Dominic Chaphuka, Joana Otoo and 
Silas Chabi for their moral support and encouragements. God richly bless you all.  
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TABLE OF CONTENTS 
DECLARATION ....................................................................................... i 
DEDICATION .......................................................................................... ii 
ACKNOWLEDGEMENTS ..................................................................... iii 
TABLE OF CONTENTS ......................................................................... iv 
LIST OF FIGURES.................................................................................. ix 
LIST OF TABLES ................................................................................... xi 
LIST OF ABBREVIATIONS AND SYMBOLS ................................... xii 
ABSTRACT ........................................................................................... xiii 
CHAPTER ONE ....................................................................................... 1 
INTRODUCTION ..................................................................................... 1 
1.1 BACKGROUND ........................................................................................... 1 
1.2 STATEMENT OF THE PROBLEM ............................................................ 2 
1.3 OBJECTIVES OF THE STUDY .................................................................. 4 
1.4 RELEVANCE AND JUSTIFICATION ....................................................... 4 
1.5 SCOPE AND DELIMITATION ................................................................... 5 
1.6 ORGANISATION OF THESIS .................................................................... 5 
CHAPTER TWO ...................................................................................... 6 
LITERATURE REVIEW ......................................................................... 6 
2.1 BASIC PHYSICS OF THE DOSE CALIBRATOR ..................................... 6 
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2.1.1 Radioactive decay .................................................................................. 6 
2.2 INTERACTION OF RADIATION WITH MATTER .................................. 8 
2.2.1 Charged particle interaction with matter ................................................ 8 
2.2.2 Interactions of Photons with Matter ..................................................... 10 
2.2.3 Gas filled detectors ............................................................................... 13 
2.2.4 The modern radionuclide calibrator ..................................................... 15 
2.2.1 Absorbed dose via measurement of current or activity ........................ 17 
2.3 CALIBRATION OF DOSE CALIBRATORS ............................................ 18 
2.3.1 Energy-response Curves (Photons) ...................................................... 19 
2.3.2 Dial value or Calibration number (NA) ................................................ 21 
2.3.3 Determining dial values for Capintec dose calibrator (Capintec 2007, 
2015). 22 
2.4 DOSE CALIBRATOR QUALITY CONTROL TESTS ............................. 24 
2.4.1 Quality Assurance and Quality Control ............................................... 24 
2.4.2 Constancy check................................................................................... 25 
2.4.3 Linearity of response test ..................................................................... 26 
2.4.4 Accuracy test ........................................................................................ 28 
2.4.5 Geometry test ....................................................................................... 28 
2.4.6 Standards relating to dose calibrators .................................................. 29 
2.5 SOME SOURCES OF ASSAY ERRORS .................................................. 30 
2.5.1 User errors ............................................................................................ 30 
2.5.2 Calibration geometry ............................................................................ 31 
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2.5.3 Effects of an external shield ................................................................. 31 
2.5.4 Effects of container material ................................................................ 32 
2.5.5 Effects of impurities ............................................................................. 33 
2.5.6 Drift in the electronics of the calibrator ............................................... 33 
CHAPTER THREE ................................................................................. 35 
MATERIALS AND METHODS ............................................................ 35 
3.1 Introduction ................................................................................................. 35 
3.2 MATERIALS USED FOR THIS RESEARCH .......................................... 35 
3.2.1 Materials and equipment ...................................................................... 36 
3.2.2 Comecer Dose Calibrator ..................................................................... 36 
3.2.3 Capintec Dose Calibrator ..................................................................... 37 
3.2.4 Standard radionuclide source ............................................................... 38 
3.3 SOFTWARE ............................................................................................... 38 
3.3.1 Microsoft Excel 2010 ........................................................................... 38 
3.3.2 Minitab 16 software ............................................................................. 39 
3.4 Methods ....................................................................................................... 40 
3.4.1 Physical inspection ............................................................................... 40 
3.4.2 Performance checks ............................................................................. 40 
3.4.3 Constancy check................................................................................... 41 
3.4.4 Accuracy test ........................................................................................ 42 
3.4.5 Linearity test......................................................................................... 42 
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3.4.6 Geometry test ....................................................................................... 43 
3.4.7 Contamination test ............................................................................... 44 
3.4.8 Other Statistical methods ..................................................................... 45 
CHAPTER FOUR ................................................................................... 46 
RESULTS AND DISCUSSIONS ........................................................... 46 
4.1 Quality Control ............................................................................................ 46 
4.2 Daily quality control .................................................................................... 47 
4.3 Constancy check .......................................................................................... 48 
4.4 Relative response check .............................................................................. 49 
4.5 Accuracy test ............................................................................................... 51 
4.6 Linearity response ....................................................................................... 52 
4.6.1 Overestimation of 99mTc assays by capintec ........................................ 55 
4.6.1 Capintec electrometer inacuracy .......................................................... 56 
4.6.2 Effects liner and/or dipper residual contamination .............................. 57 
4.7 Geometry test .............................................................................................. 59 
4.8 CHOOSING REFERENCE DOSE CALIBRATOR FOR CROSS 
CALIBRATION .................................................................................................... 64 
4.8.1 137Cs Calibration factor (CF) ................................................................ 65 
4.9 Cross-calibration curve for 99mTc assays on Capintec with Comecer as the 
reference dose calibrator. ...................................................................................... 67 
4.9.1 Validation of 9mTc calibration curve .................................................... 69 
4.10 Determination of new dial value (N ) for 99mTc and 137A Cs on Capintec ..... 70 
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4.10.1 99m Tc new dial value (NA) on Capintec ................................................ 71 
4.10.2 137 Cs dial value (NA) on Capintec ........................................................ 73 
CHAPTER FIVE ..................................................................................... 75 
CONCLUSION AND RECOMMENDATIONS ................................... 75 
5.1 Conclusion ................................................................................................... 75 
5.1.1 Recommendations ................................................................................ 75 
5.1.2 Nuclear Medicine Department ............................................................. 76 
5.1.3 Nuclear Regulatory Authority and Radiation Protection Institute ....... 76 
5.1.4 Research Community ........................................................................... 76 
REFERENCES ........................................................................................ 77 
APPENDIX ............................................................................................. 81 
 
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LIST OF FIGURES 
Figure 2.1: Schematic representation for charged particle interactions. .................... 10 
Figure 2.2: The three major photon interactions with matter for   different energies.11 
Figure 2.3: Graph showing the variation of the pulse height  with  voltage Vdc . ...... 14 
Figure 2.4:  Schematic representation of a dose calibrator ........................................ 15 
Figure 2.5: Radionuclide calibrator............................................................................ 16 
Figure 2.6: Energy-response curve using Co-60 as standard source. ........................ 20 
Figure 3.1: Some materials used for the study ........................................................... 35 
Figure 3.2: FHG LAF shielded Radiochemistry Cappa/fume hood with Comecer 
dose calibrator. ........................................................................................ 37 
Figure 3.3: Capintec CRC-15R dose calibrator ......................................................... 37 
Figure 3.4: Vial containing 137Cs standard radionuclide source ................................ 38 
Figure 3.5: Interface for Microsoft Excel 2010 ......................................................... 39 
Figure 3.6: Interface for Minitab 16 software ............................................................ 40 
Figure 4.1: (a) Graph of activity against number of weeks for constancy check (b) 
Relative deviation against number of weeks for constancy check on 
Comecer and Capintec dose calibrators. ................................................. 49 
Figure 4.2: (a) Relative response test for Comecer and (b) Relative response test for 
Capintec   using 137Cs standard radionuclide source. .............................. 50 
Figure 4.3: (a) Measured 137Cs activity against number of weeks (b) Deviations of 
measured activity about the true activity of 137Cs standard radionuclide 
source. ..................................................................................................... 51 
Figure 4.4: Decay curves for 99mTc activities on Capintec and Comecer dose 
calibrators. ............................................................................................... 54 
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Figure 4.5: Linearity response for Capintec and Comecer dose calibrators on 
logarithmic scale. .................................................................................... 54 
Figure 4.6: (a) % of 99mTc activity overestimated by Capintec over entire range of 
activities used and  % of 99m(b) Tc activity overestimated by Capintec 
over useful clinical range. ....................................................................... 55 
Figure 4.7: Drifts in Capintec electrometer readings ................................................. 56 
Figure 4.8: Effects of residual contamination for Capintec ....................................... 57 
Figure 4.9: Dipper and liner contamination levels for Capintec ................................ 58 
Figure 4.10: Volume correction factor against sample volume for Comecer and 
Capintec dose calibrators using a 10ml vial. ........................................... 60 
Figure 4.11: (a) Activity against source volume for vial (b) Error due to volume of 
source in vial. .......................................................................................... 60 
Figure 4.12: VCF against sample volume for the 2ml syringe. ................................. 62 
Figure 4.13: The influence of Source container and sample volume on assayed 99mTc 
activity within 2% and 5% uncertainties. ................................................ 63 
Figure 4.14: Normalized 137Cs activity against number of reading within 5% error 
margin...................................................................................................... 65 
Figure 4.15: Error due to 137Cs calibration factor. ..................................................... 66 
Figure 4.16:  Calibration curve for Capintec with Comecer as reference dose 
calibrator over entire range of 99mTc source activities used. ................... 67 
Figure 4.17:  Calibration curve for Capintec with Comecer as reference dose 
calibrator over useful clinical range of 99mTc source activities. .............. 68 
Figure 4.18: Error due to old and New dial values for 99mTc assays on Capintec. .... 72 
 
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LIST OF TABLES 
Table 2.1: Specifications for two common radionuclide calibrators………………17 
Table 2.2: Dose calibrator quality control tests ……………………………………25 
Table 2.3: Limits of acceptability for different standards for dose calibrators ……30 
Table 3.1: Specifications for Capintec CRC-15R and Comecer dose calibrators… 36 
Table 4.1: Physical inspection…………………………………………………….. 46 
Table 4.2:  Daily tests on Capintec …………………………………………………47 
Table 4.3: Daily tests on Comecer ………………………………………………....48 
Table 4.4:  Constancy check …………………………………… ………………....48 
Table 4.5: Relative response of calibrators to 137Cs radionuclide source ……….....49 
Table 4.6: Accuracy of Comecer and Capintec …………………………………....51 
Table 4.7: Linearity response for Comecer to 99mTc radionuclide source…...…….52 
Table 4.8: Linearity response for Capintec to 99mTc radionuclide source…..…..…53 
Table 4.9:  Geometry dependence for Comecer and Capintec dose calibrators …..59 
Table 4.10: Further vial geometry test for Comecer and Capintec ……………….61 
Table 4.11: Measurements accuracy with Comecer dose calibrator……………... 64 
Table 4.12: Measurements accuracy with Capintec dose calibrator……………... 64 
Table 4.13: Excel validation of 99mTc calibration ……….. ……………………....69 
Table 4.14: Minitab validation of 99mTc calibration ………..………………….... 70 
Table 4.15: Old and new dial value for 99mTc on Capintec ……………………....71 
Table 4.16: Practical range of 99mTc  dial value on Capintec ……………….…....72 
Table 4.17: New dial value for 137Cs on Capintec………………………………. 73 
Table 4.18: Practical range of 137Cs  dial value …………………..………….…...74 
 
 
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LIST OF ABBREVIATIONS AND SYMBOLS 
99m
Tc                            Technetium 99m 
Cs-137                          Cesium 137 
eV                                  Electron volt 
GBq                              Gigabequerel 
KeV                               Kiloelectron volt 
mCi                                Millicurie 
MBq                               Megabequerel 
AAPM                           American Association of Physicists in Medicine 
ANSI                              American National Standards Institute  
IAEA                             International Atomic Energy Agency  
IEC                                International Electrotechnical Commission 
NCRP                            National Council on Radiation Protection and Measurements 
NIST                              National Institute of Standards and Technology  
NPL                               National Physical Laboratory 
QA                                 Quality Assurance 
QC                                  Quality Control 
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ABSTRACT 
Dose calibrators are used for accurate measurement of radionuclide activity which is 
required to achieve the desired efficacy for the best clinical outcome. Observations 
from assayed activity with Capintec and Comecer dose calibrators at the nuclear 
medicine department of the Korle-Bu Teaching Hospital have indicated that the two 
systems report significantly different (>10%) readings for the same activity source. 
Also unusually high background readings (>20% of the mean) have been noted at the 
137Cs and 99mTc radionuclide settings for Capintec. The study therefore investigated 
the reasons for these observations so as to cross-calibrate the two systems to enable 
accurate measurements of radionuclide sources. Constancy check with 137Cs standard 
radionuclide source found Comecer and Capintec systems to have standard 
deviations of 1.2% and 0.74% respectively.The study also revealed deviations within 
±5% tolerance for relative response to 137Cs standards at clinically significat 
radionuclide settings for both systems. The results for accuracy in the measurement 
of 137Cs standards for Comecer and Capintec systems  were found to be 185.1 µCi 
±1.4% and  193.7 µCi ±3.1% respectivey. Using constant activity method, both vial 
and syringe geometry testing yielded uncertainties within ±2% tolerance for both 
systems. Linearity response for both systems yielded deviations within ±5% 
tolerance. 
However, the study revealed underestimation with Comecer and overestimation with 
Capintec for 99mTc assays below 1 mCi by 13-16% and 11-31% respectively. The 
study also found evidence of residual contamination for Capintec systems within 
tolerance levels. A calibration curve was developed to determine theoretical activities 
of 99mTc on Capintec with Comecer as the reference dose calibrator and the results 
gave assay accuracy within ±5% tolerance levels.  Investigation of the influence of 
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dial values supplied by Capintec on the measured activity readings on their system 
found drifts in the gain settings to be the reason for higher measurement readings as 
compared to Comecer system. However, new dial values were theoretically 
determined and the gain setting was adjusted to give assay accuracy within ±5% 
tolerance for 99mTc and 137Cs sources. Performance evaluation and cross-calibration 
have been done on Capintec and Comecer dose calibrators. The study revealed 
variations in the performance of both systems within tolerance levels recommended 
by standard protocols using appropriate settings and procedures (AAPM Report 181, 
2012, IAEA TRS 454, 2006, ANSI N42.13 2004, and IAEA-TECDOC-602, 1991). 
 
 
 
 
 
 
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CHAPTER ONE 
INTRODUCTION 
1.1 BACKGROUND 
Nuclear medicine is the branch of medical imaging that uses small amounts of 
radioactive materials for diagnosis, staging of disease, therapy and monitoring the 
response of a disease process (Bailey et al, 2014). The tracer principle is used in 
nuclear medicine because of its ability to utilize small amounts of radioactive 
substance in living organisms without significant pharmacological effect on the 
body. The practice of nuclear medicine involves administering small amounts of 
radio-labeled compounds called radiopharmaceuticals. The radiopharmaceutical 
administered to the patient orally, intravenously or by inhaling localizes in the target 
cell for either diagnostic or therapeutic purposes. Diagnostic radiopharmaceuticals 
yield information about where they are localized which can help imaging of the 
organ of interest in patient using special gamma cameras such single photon 
emission tomography (SPECT) or positron emission tomography (PET) imaging 
system. On the other hand, therapeutic compounds target specific tumors, such as 
thyroid, lymphomas or bone metastases, delivering radiation to tumorous lesions for 
the purpose of curing, destroying, mitigating or controlling the disease (Bailey et al, 
2014 and Cherry et al, 2012). 
The activity of a radiopharmaceutical is accurately assayed with the use of a dose 
calibrator (radionuclide dose calibrator). The accuracy of measurements should be 
covered by consistent quality control of the instrument, including a daily constancy 
test, a quarterly linearity test, an annual accuracy check and periodic reassessment of 
its calibration, traceable to secondary standards (IAEA TRS 454, 2006).  
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Tyler and Woods (2003) report that it is a good practice to re-measure syringe 
activity while taking into account geometry dependence so as to administer the 
correct activity to patients. To reduce the error due this geometry, volume correction 
factors have to be derived for several medically important radionuclides.  
Clinically, a lower than actual activity implies that, the patient will be given a higher 
than prescribed dosage activity being unnecessarily burdened with extra radiation. 
On the other hand, a higher dosage of administered activity will be inadequate, 
demanding repetition of the process which implies extra dose to the patient and 
occupationally exposed staff. Quality control is therefore critical if the dose 
calibrator is to be used effectively. A nuclear medicine facility should therefore 
ensure dose calibrators are regularly checked for any calibration errors to ensure that 
assay errors of prescribed dosage fall within recommended limits (Khan et al, 2016). 
The International Atomic Energy Agency (IAEA) recommends an assay accuracy of 
±5% while the American National Standards Institute (ANSI) recommends ±10% 
assay accuracy for a radionuclide dose calibrator. In most countries, the limit is for a 
given dose to fall within ±10% of the prescribed dosage (IAEA TRS 454, 2006 and 
ANSI N42.13, 2004). 
 
1.2 STATEMENT OF THE PROBLEM 
Accurate measurement of radionuclide activity is required to achieve the desired 
efficacy and for the best clinical outcome. Although some manufacturers of the dose 
calibrators claim high accuracy and reproducibility for the radioactivity 
measurements, yet few studies have reported variations in these parameters (Sharma 
et al, 2015). 
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Bailey et al (2014) reports errors ranging from 64 to 144% of the expected activity 
using calibration factors supplied by manufacturers of radionuclide dose calibrators. 
This re-emphasized the need for consistent quality assurance programme to confirm 
calibrations within a Nuclear Medicine unit. 
Other researchers have reported differences in assayed activity for VDR-15R and 
CAPINTEC CRC®-25R calibrators within ± 10% tolerance as required by well-
established international standards. To maintain the effective use and proper function 
of the dose calibrator, a further evaluation criterion was recommended to include a 
daily constancy check, an annual accuracy check and a quarterly linearity test (Assan 
et al, 2012 and IAEA TRS 454, 2006). 
The nuclear medicine department of the Korle-Bu Teaching Hospital has Capintec 
CRC®-15R and Comecer radionuclide dose calibrators.  Observations from assayed 
activity have indicated that the two systems report significantly different (>10%) 
measurement readings for the same activity source. This study therefore seeks to 
investigate the reasons for these observations so as to cross calibrate the two systems 
to enable accurate measurements from any of them. The overall performance of the 
two systems will also be assessed and evaluated through accuracy, constancy, 
geometry and linearity quality control tests. 
 
 
 
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1.3 OBJECTIVES OF THE STUDY 
The principal objective of the study is to cross calibrate CAPINTEC ®  CRC 15R and 
COMECER dose calibrators in use at the Nuclear Medicine Department of Korle-Bu 
Teaching Hospital. The specific objectives are: 
1.  To assess the performance of Capintec and Comecer dose calibrators.  
2.  To establish calibration factors for accurate measurement of radionuclide 
activity on the two systems. 
3.  To re-calculate dial values for some clinically significant and available 
radionuclides. 
 
1.4 RELEVANCE AND JUSTIFICATION 
Dose calibrators are very important in the practice of nuclear medicine. Their proper 
use requires a comprehensive quality assurance program to assure the nuclear 
medicine practitioner that the doses of radioactive materials being administered to 
the patients are sufficient for the task and do not harm the patient. It is in light of this 
that the work undertaken in this thesis is important. It is an attempt to evaluate the 
performance of dose calibrators in the Nuclear Medicine Unit of Korle Bu Teaching 
Hospital, especially in the absence of a rigorous programme of maintenance and 
calibration of such equipment in the country. 
Results from the comprehensive quality control tests on Capintec and Comecer 
radionuclide dose calibrators will serve as an integral component of a quality 
assurance programme at the nuclear medicine department of the Hospital. The study 
will provide specifically derived calibration and volume correction factors which 
would be used for future reference by nuclear medicine personnel. The calibration 
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curve/equation from cross calibration between the two systems will be available to 
help provide a means of ensuring the correct activity is administered to patients even 
in the case where one of the radionuclide dose calibrators develops a fault. The cross-
calibration will in itself be a quality control measure and serve as double check on 
radionuclide activity to be administered. Finally, results and recommendations from 
the study will be valuable to the Nuclear Regulatory Authority for quality assurance 
audits and also serve as benchmark for further research. 
1.5 SCOPE AND DELIMITATION 
The research was done at the nuclear medicine department of the Korle-Bu Teaching 
Hospital in Accra within the period September 2017 to July 2018. The study covers 
general QC tests (accuracy, constancy, linearity and geometry) performed on 
Capintec and Comecer dose calibrators. The research also investigated the influence 
of predetermined dial values on the assay accuracy of Capintec radionuclide dose 
calibrator. 
1.6 ORGANISATION OF THESIS 
The thesis consists of a chronological order of five chapters. Chapter one describes 
the general background to the research, provides an overview of the existing state of 
knowledge relevant to the study and gives the organization of the thesis. The 
literature relevant to the research problem is reviewed in chapter two. Chapter three 
focuses on the materials and methodology of the study. The results obtained are 
presented and discussed in chapter four. Chapter five covers the conclusions and 
recommendations from the study. The references section contains citations of other 
researches and papers relevant to the study. An appendix section is also given for 
details on the data collected. 
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CHAPTER TWO 
LITERATURE REVIEW 
2.1 BASIC PHYSICS OF THE DOSE CALIBRATOR  
2.1.1 Radioactive decay 
Radioactive decay is the process in which an unstable nucleus releases matter and/or 
energy during a transition to a more stable form. It may do so by releasing sub-
atomic particles and energy, or by capturing an orbital electron into its nucleus thus 
releasing energy. Atoms that are unstable are also known as radioactive atoms, or 
radionuclides. The original, radioactive atom is known as the parent. The new 
nucleus (after decay) is known as the daughter radionuclide. The activity of a 
radioactive source is the number of disintegrations per second. The SI unit of activity 
or decay rate is the Becquerel (Bq). The Curie (Ci) is the traditional unit for 
radioactivity and it approximates the disintegration given out every second by 1g of 
radium in a state of equilibrium with daughter nuclei (Maher et al, 2006).  
1Ci  3.71010 Bq  
1Bq 1ds1  
Although radioactivity is a random and spontaneous process each radionuclide 
decays at its rate, having its own decay constant (λ).  
dN
                                          N                                                          (2.1.1) dt
The negative sign shows that the number of nuclei N decreases as time elapses. The 
activity of a radioactive source A is given by the quantityN . 
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The strength of a radioactive source is therefore given by its activity. The solution to 
first order equation (2.1.1) above is the following function: 
t
                                     N(t)  N0e                                             (2.1.2) 
Where, N (t) is the number of nuclei present at time t and N0  is the initial number of 
nuclei at t0 respectively. From above, the activity can therefore be written as 
t
                                    A(t)  A0e                                              (2.1.3) 
Where, A(t) is the activity at time t and A0  is the initial activity at t0 respectively. 
The process of decay is random for individual atoms. Although the exact moment of 
an individual atomic decay cannot be predicted, the probability of decay during a 
given time period can be measured (based on observations from a large number of 
atoms). The decay constant (λ) is expressed in units of probability per unit time 
(Cherry et al, 2012 and Maher et al, 2006). 
The half-life     is the time required for 50% of the parent atoms to undergo 
 
radioactive decay. Substituting      and N(t)  0.5N0  into (2.1.2) gives the relation 
 
between the half-life and decay constant ( ): 
                                                                                                         (2.1.4)                                 
  
Where   is the mean lifetime, defined as the time taken for the nuclei to decay to 
1 N . Also substituting (2.1.4) into (2.1.3) yields; 
e 0
 
   
                                    ( )    ( )     ( )                                              (2.1.5)   
Where n is the number of half-lives. 
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2.2 INTERACTION OF RADIATION WITH MATTER 
 
Ionizing radiation can be classified into either particulate type (α particle, β particle, 
etc.), or non-particulate type, such as high-frequency electromagnetic radiation (e.g., 
γ rays, X-rays, etc.), and both kinds are ionizing radiations. As shown in Figure 2.1, 
the mechanism of interaction of the two types of radiations with matter is different 
and forms the basis on which activity is measured (Cherry et al, 2012 and Maher et 
al, 2006).  
 
2.2.1 Charged particle interaction with matter 
Alpha-particle radiation (α-particle): Alpha radiation is identical to a helium 
nucleus ( 42 He ).  The α-particle is positively charged (+2e) heavy nucleus, with short 
range in air, has low penetration and mostly emitted by a radionuclide with energy 
less than 10MeV. The low penetration makes the α-particle hard to detect. All α-
decays go with the emission of photon radiation as the daughter nucleus de-excites. It 
is this emitted photon that makes it possible to measure activity of a nuclide (Cherry 
et al, 2012). 
 
β+ Radiation ((positron):β+ particle originates from the nucleus of an atom when a 
nucleus has too few neutrons relative to protons. A proton is converted into a neutron 
while releasing a β+ particle is emitted along with some energy. it loses its kinetic 
energy mainly through direct-ionization and then annihilates with its anti-particle 
(electron) to produce two 511keV photons in opposite directions (almost at 1800 with 
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each other). These photons associated with β+ decay makes it easy to detect β+ 
radiation .β+ decay is also associated with de-excitation photons (Powsner et al, 2013 
and Cherry et al, 2012).  
 
β- Radiation: a β-particle is a fast moving electron. This electron is ejected from the 
nucleus and mainly loses its kinetic energy by direct ionization. The range of most 
emitted β's is short. It should be noted that in β+ and β-emission, the emitted electron 
or positron has a continuous energy spectrum, which ranges from the maximum 
transition energy Emax to zero. β-radiation (except a few high energy βs) is easily 
stopped in a material. As shown in Figure 2.1, the electron loses energy and 
continuous low energy photons are emitted. The emission is referred to as 
Bremsstrahlung. Many radionuclides that decay by β emission also emit de-
excitation photons (x-rays, γ-rays), which can be detected to measure the activity of a 
sample (Powsner et al, 2013 and Cherry et al, 2012). 
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Figure 2.1: Schematic representation for charged particle interactions. 
 
Source: Physics in Nuclear Medicine by Cherry et al, 2012, p.64 E-Book: Elsevier 
Health Sciences. 
 
 
A represents Photon interaction with an outer electron resulting into ionization and  
B, Interaction with a nucleus, resulting in bremsstrahlung production (Cherry et al, 
2012).  
 
2.2.2 Interactions of Photons with Matter 
The energy of a photon is the major determinant of the mechanism by which it 
interacts with matter. The three main modes by which photons interact with matter to 
deposit their energy are discussed and illustrated in Figure 2.2 below. The boundaries 
show the values of Z and photon energy for which the effects are just equal. 
 
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Figure 2.2: The three major photon interactions with matter for different energies.   
Source: Physics in Nuclear Medicine by Cherry et al, 2012, p.81 E-Book: Elsevier 
Health Sciences. 
Photoelectric Effect: In photoelectric effect an incoming photon interacts with and 
an electron which is bound to the atom.  During this process, the photon is absorbed 
by the atom and an electron is ejected. The kinetic energy with which the photo-
electron is ejected is equal to the difference between the energy of the incoming 
photon energy and the binding energy of the electron. In nuclear medicine, the 
photon energies of interest are between 30 and 300kev. This is due to the fact that, at 
these energies the electrons are more penetrating and thus able to participate in the 
photoelectric process. The photoelectric effect is therefore pre-dominant at low 
energies (interactions vary inversely as the third power of the energy). However, as 
photon energies become greater than the electron binding energies, the probability of 
the photoelectric process diminishes. At a certain energy, the number of photoelectric 
interactions per unit mass varies as the fourth power of the atomic number and is 
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inversely proportional to the atomic weight of the medium (Z4/E3A) (Powsner et al, 
2013 and Cherry et al, 2012). 
Compton Effect: The Compton Effect is the interaction of a photon with a free 
electron. If the energy of the incoming photon is much greater than the binding 
energy of the electron, the electron is said to be a free (unbound). The kinetic energy 
of the electron that is scattered is dependent upon the angle through which it is 
scattered. In order to impart all its energy to the medium, the scattered photon must 
continue to interact with the medium.  
Compton Effect is pre-dominant for high photon energies (ranging from 100 keV to 
10 MeV) for atomic numbers for detector materials. At 100 keV, the maximum 
kinetic energy of the scattered electron is about 30 % of the incoming photon; at 1 
MeV, it is about 80 %; and at 10 MeV, about 98%. The number of Compton 
interactions per unit mass is approximately proportional with the energy the 
incoming photon and atomic number but inversely proportional to the atomic weight 
of the medium (ZE/A) (Cherry et al, 2012).  
Pair Production: In the presence of the nuclear field, the incoming photon 
disappears and an electron-positron pair is produced. This process is called pair 
production. In order to produce an electron-positron pair, the incoming photon 
energy must be at least greater than 1.022 MeV (twice the mass of an electron). Pair 
production is pre-dominant at very high energies, that is, above about 10 MeV. The 
number of pair production interactions per unit mass is proportional to the square of 
the atomic number and inversely proportional to the atomic weight of the medium 
(Z2E/A) (Powsner et al, 2013 and Cherry et al, 2012). 
 
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2.2.3 Gas filled detectors 
As already seen above, the creation of ions is one of the results from the interaction 
of radiation with matter. This outcome is utilized by gas-filled detectors. In gas-filled 
detectors, the atoms of a gas are ionized by the radiation. Thus, the detector is the gas 
and can be used to measure radiation fields if the relationship between the radiation 
field and the charge produced is known. The radiation enters the detector and 
interacts with the gas or with the walls of the chamber. It must be pointed out that 
photons cannot produce ionization directly, but must first interact with the chamber 
material (gas and wall) to produce electrons (Maher et al, 2006).  
That is, through a series of interactions, the photon transfers its energy to one or 
more electrons. The electron is slowed down through collisions with the chamber gas 
(argon). The collisions knock electrons off the molecules producing positive ions 
(this is the ionization process). An electric field is set up by the collection voltage 
across the chamber as positive ions drift towards the cathode and the electron drifts 
towards the anode, thus producing a current. The electronic circuitry then measures 
either the current or the total charge produced during the period of interest (Bailey et 
al, 2014 and Maher et al, 2006). 
A gas-filled detector is commonly cylindrically shaped, with a well-insulated outer 
wall from a central electrode.  Depending on the design of the detector and the 
voltage Vdc  applied across the  electrodes, its operation can fall in any of three 
regions (i.e. the ionization region B, proportional region C or Geiger–Müller (GM) 
region D) shown in Figure 2.3 below (Maher et al, 2006).  
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Figure 2.3:  Graph showing the variation of the pulse height with voltage Vdc .  
Source: Basic Physics of Nuclear Medicine by Maher et al, 2006, p.58. Libronomia 
Company:  Wikibooks. 
 
 
As be seen in Figure 2.3, the graph is divided into five main regions;  
Region A: Here Vdc is very low and recombination of the electrons and positive ions 
takes place. Consequently, the pulse height is small due to the insufficient collection 
of ion pairs. As the applied voltage increases, recombination diminishes (Maher et al, 
2006). 
 Region B: Vdc is appreciably high in this region so recombination is almost 
negligible. This region is called the ionization region and this is the operation region 
for a type of gas filled detector called ionization chamber. This is the region in which 
dose calibrators operate.  
Region C: Vdc is sufficiently great to cause the electrons approaching the central 
wire to gain sufficient energy for collisions with the gas atom electrons to produce 
more ion pairs. Consequently, the number of electrons is increased so that the charge 
through the resistor may be very high (i.e. in the orders of thousand times) compared 
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to the charge produced primarily by the radiation interaction. A detector known as 
proportional counter operates in this region (Maher et al, 2006 and Podgorsak, 2005).  
Region D: Vdc is so huge that even a weakly-ionizing particle creates a large voltage 
pulse. The primary ionization brought about by the radiation causes a complete gas 
breakdown as an avalanche of electrons drift towards and spreads along the central 
wire. This region is referred to as the Geiger-Müller Region and the detector that 
utilizes this it is called Geiger counter.  
 Region E: This region cannot be used for the detection of radiation events since any 
further rise in Vdc is sufficient enough to completely cause gas breakdown (Maher et 
al, 2006). 
 
2.2.4 The modern radionuclide calibrator 
  Figure 2.4:  Schematic representation of a dose calibrator 
 
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The calibrated re-entrant ionization chamber is commonly referred to as a dose 
calibrator. The instrument is able of provide accurate radioactivity measurements 
within clinically acceptable levels when properly calibrated, operated, and serviced. 
The chamber is typically made of aluminum enclosed with argon under pressure (1-2 
MPa or 10-20 atm). It has a perspex well lining material easily removable for 
cleaning to prevent the chamber from accidental contamination. A vial holder 
(dipper) into which a syringe or vial is placed is provided to maintain the source 
geometry and ensure optimal positioning within the chamber. The chamber is 
normally pre-shielded with 6mm of lead by the manufacturer in order to lower the 
influence of background radiation IAEA-TECDOC (1991). 
  
 
Figure 2.5: Radionuclide calibrator 
Source: Essentials of Nuclear Medicine Physics and Instrumentation by Powsner et 
al, 2013, p.48. John Wiley & Sons. 
 
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Table 2.1 shows some specifications for two common radionuclide dose calibrators. 
Table 2.1: Specifications for two common radionuclide calibrators 
Specification Capintec CRC-25R Atomiclab 200 
Ionization chamber 26cm deep×6cm diameter 26.7cmdeep×7cm diameter 
dimensions 
Measurement range  Auto ranging from Auto ranging from 0.001MBq 
0.001MBq to 250GBq to 399.9GBq 
Nuclide selection 8 pre-set, 5 user-defined 10 pre-set, 3 user-defined 
(80radionuclide (94radionuclide calibrations in 
calibrations in memory) manual) 
Display units Bq or Ci Bq or Ci 
   
Electrometer accuracy <±2% <±1% 
   
Response time Within 2s 1s for activities >75MBq 
   
Repeatability ±1% ±0.3% 
Source: Nuclear Medicine Physics: a Handbook for Teachers and Students by Bailey 
et al 2014, p.252. Vienna: International Atomic Energy Agency (IAEA). 
 
2.2.1 Absorbed dose via measurement of current or activity  
People or biological systems exposed to radiation are at potential risk of radiation 
dose being delivered. The quantity of energy deposited per unit mass is the absorbed 
dose. It is therefore important to distinguish between the activity of a radioactive 
source and the radiation dose which may result from the source. The radiation dose 
depends on the location of the source with regard to those exposed. Furthermore, the 
radiation dose depends upon the type of radiation, such as whether it is α, β or γ-rays 
and the energy of the radiation. The energy is transferred in small quantities for each 
interaction between the radiation and a molecule and there are usually many such 
interactions. Radiation results in the formation of positive and negative ions in a gas 
as well as in all other materials (Bailey et al, 2014). 
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When a syringe or vial enclosing the radioactive sample is placed into the source 
holder and gently lowered into the chamber, the inactive gas is ionized; ion pairs drift 
towards opposite polarity thus setting up an electrical current. This current between 
the electrodes is proportional to the activity of the assayed radioisotope. The 
magnitude of this current is usually small (on the microampere level) even if higher 
activity is used. It is for this reason that an electrometer is coupled to the dose 
calibrator in order to quantify this minimal electric current and convert the display 
into activity in MBq or mCi (Bailey et al, 2014 and Powsner, 2013).  
 
2.3 CALIBRATION OF DOSE CALIBRATORS 
Calibration involves the determination of a numerical relationship, with its associated 
uncertainty, between an observed measurement and its expected value using a 
standard system, based on reference sources, traceable to national primary standards 
of radioactivity. Traceability is the characteristic of  a result or value of a standard by 
which it can be linked to some references, normally national or international 
standards, through a continuous chain of assessments, all having defined 
uncertainties (Gagnon et al, 2010 and Gadd et al, 2006). 
Calibration of dose calibrators may also involve determining dial settings for each 
radioisotope to be assayed. Manufacturer calibration settings are given as dial 
settings (calibration factors) for individual radionuclides. However, these settings 
may vary slightly because the chamber response depends on the type of radionuclide, 
its geometry (source vessel type and volume) and height in the chamber. Therefore, 
in order to ensure accurate measurement for each radionuclide, the assay must be 
made using the appropriate calibration setting and correct geometry for which the 
system was calibrated (AAPM Report 181, 2012 and Gadd et al, 2006). 
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Sharma et al (2015) reported a cumulative error of about 20.0% with respect to the 
accuracy in the measurement of radioactivity for the beta‑gamma emitters.  There is 
consequently the need to redefine the manufacturers’ quoted values of the calibration 
settings of the dose calibrators used in a given hospital‑based clinical setting.  
Although most dose calibrator are purchased pre-calibrated by the producer for 
frequently used radioisotopes, the dial values need periodical review as they are 
originally determined through measurements of primary or traceable standard 
sources for a master system before they are transferred to a production system as 
calibration settings. The settings can also be calculated using energy-response curves 
obtained using available decay schemes. It is recommended for medical facilities, 
radiopharmaceutical companies or commercial nuclear pharmacies to occasionally 
review and verify if these calibration settings are traceable to NIST standards 
(AAPM Report 181, 2012). 
Tyler and Woods (2003) report significant  differences between the dial values for 
syringes and glass vials due to different energy photon emissions from the decay of 
the radionuclides; the lower the energy, the greater the difference. Large differences 
were observed for 125I and only small differences for 131I. However, for radionuclides 
such as 99mTc and 67Ga, variations of up to 30% have been observed indicating the 
importance of specifically derived calibration factors as well as emphasizing the 
complexity of the problem with regard to geometry influence. 
2.3.1 Energy-response Curves (Photons) 
Calibration settings for the chamber can be determined for individual radionuclides. 
The energy efficiency N , of the ionization chamber for a radioactive source is given 
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by the reciprocal of the calibration setting and can be written as the summation of 
two components: 
 N Pi Ei  i Ei                                              (2.3.1) 
                              i
Where 
 
 Pi Ei   is the emission probability for each disintegration of photons with energy Ei  
and  i Ei   is the  efficiency of the  chamber. A number of calibration coefficients are 
obtained using well known reference sources within required energy window. The 
chamber’s response as a result of particular photons from the radioisotope is then 
determined, standardized to a reference source, and plotted to obtain the energy-
response profile. Figure 2.6 below shows a characteristic curve using 60Co as 
standard source for an aluminum alloy wall ionization chamber for a commercial 
radionuclide dose calibrator (Bailey et al, 2014 and AAPM Report 181, 2012).  
 
Figure 2.6: Energy-response curve using 60Co as standard source. 
Source: AAPM Report TG 181, 2012, p.10. 
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For aluminum-walled chambers, photons with energies around 13 keV are blocked 
from reaching the sensitive volume of the chamber. The actual threshold varies 
depending upon the source container wall material, its volume and thickness. The 
thickness differs from system to system due to manufacturing discrepancies. As seen 
in Figure 2.6, from a low-energy cut-off, ionization current rises sharply and then 
falls suddenly, producing a peak at roughly 50 keV. The peak is as a result of the 
opposing effects that a rise from photon transmission through the source, container 
and chamber wall (since photoelectric effect falls sharply), together with the 
subsequent reduction in photon interaction with the chamber volume. Compton 
scatter dominates at almost 50 keV. Above 200 keV Compton scatter is predominant 
and the response rises with increase in photon energy.  Thus, efficiency is minimal at 
low energies, has a peak around 50 keV, drops to a minimum at 200 keV, before 
increasing proportionally to energy (Bailey et al, 2014 and AAPM Report 181, 
2012).  
2.3.2  Dial value or Calibration number (NA) 
The dial value or calibration number (  ) is the factor dialed into the calibrator to 
give the desired gain. A calibration number helps to convert the measured current to 
a nominal activity. This means that a dose calibrator requires a different dial value 
for each individual radioisotope to be measured (Prekeges, 2012). 
The size of a calibration factor is also determined by the chamber (thickness of inner 
wall, pressure of the gas, design, and applied voltage), geometry of source (vessel 
type, thickness, its volume) and location of the sample in the chamber (Prekeges, 
2012 and Capintec 2007).   
 
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2.3.3 Determining dial values for Capintec dose calibrator (Capintec 2007, 
2015). 
It is very convenient to express the response    of the detector to a radioisotope, N, 
relative to that of a standard reference material (SRM), e.g. Co-60. 
                              
( )
                   
                                                  (     )                                 
( )
                               
The sensitivity    of the detector for a photon of energy    is defined as: 
                                             
                                   (     )                                         
The detector response    and the sensitivity have the following relation: 
                                   ∑                                                                               (     ) 
 
Where    is the intensity of the photon whose energy is   . 
The relationship between the response of the detector and the gain setting    
(relative to that for 60Co, in order for the instrument to give a direct reading of the 
activity) is given by: 
 
                                                                                                                       (     )   
Capintec calibrators are calibrated with certified Cobalt-60 and Cobalt-57 standard 
radionuclide sources. The calibration setting number    of Capintec Calibrators for a 
radioisotope A, is given by 
                          
   (   (  )        )  ( )       (     )                           
Where:  
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NCo-60 and NCo-57, and RCo-60 and RCo-57 are the calibration numbers and responses for 
60Co and 60Co standard radionuclide sources respectively. For Capintec these are 
assigned the following numbers: 
 NCo-60 = 990, NCo-57 =112   
            ,                  
 Substituting the values for NCo-60 and NCo-57, and RCo-60 and RCo-57 into equation 
(2.3.6) equation (2.3.7) below is obtained: 
                                             (        )                                                 (     ) 
However, as seen in equation (2.3.5) the gain    is inversely proportional to the 
response   , we can therefore rewrite (2.3.7) as: 
 
                                                                                                      (     )   
         
The accuracy of the sensitivity curve and calibration number determined are tested 
by calculating calibration numbers for all radioisotope standards used for the studies 
of the sensitivity. The agreement between the calculated and observed responses 
should be within ±3% tolerance (Capintec 2007, 2015). 
 
 
 
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2.4 DOSE CALIBRATOR QUALITY CONTROL TESTS   
2.4.1  Quality Assurance and Quality Control 
For dose calibrators quality Assurance (QA) is a systematic tool for checking and 
evaluating the attainment of high standards of efficiency and reliability in the 
practice. It encompasses management plans to guarantee the dependability of the 
production system. QA helps in minimizing the uncertainties and errors in equipment 
performance. Quality Control (QC) refers to the specific measures put into place to 
ensure that each particular aspect of the procedure is reliable (IEC TR 61948-4, 2006 
and IAEA-TECDOC, 1991). 
 Specifically, QC is part of the QA programme and is essential for the submission of 
requirements for procedures; the preparation and administration of 
radiopharmaceuticals. QC is essential for radiation protection of patients, staff and 
the general public. It also serves as an important component in the preparation of 
patients; the setting-up, use and repairs of electronic devices; the method of the 
actual procedures; the investigation and interpretation of images; the reporting of 
results and, finally, for record keeping . A radionuclide dose calibrator must therefore 
be covered by a comprehensive QA programme. It is important to carry out the test 
procedures correctly since the safety of the patient is highly reliant on the accuracy 
of measurements from the radionuclide dose calibrator. Often, procedural errors in 
performing QC on calibrators seem to be unavoidable even by experienced users. It 
is therefore important to adhere to guidelines given in the user manual. The QC tests 
performed on dose calibrators are shown in Table 2.2 (IAEA TRS 454, 2006 and 
IAEA-TECDOC, 1991).  
 
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Table 2.2: Dose calibrator quality control tests   
QC test Frequency Source  Half-life Energy (keV) 
Constancy Daily 137Cs 30 years 662 
Check 
     
Linearity Installation, quarterly,     
response After repairs and 99mTc 6hours 140 
test  when displaced to new  
location. 
     
Accuracy Installation, annually 60Co 5.3years 1170, 1330 
test  and after repairs.     
 137Cs 30 years 662 
   
133 10.51 years 356 
Ba 
   
57 271.7 days 122 
Co 
     
Geometry Installation and after 99m 6 hours 140 
test repairs.  Tc 
 
 
2.4.2 Constancy check 
Constancy means reproducing a measurement result whenever the same source is 
assayed over a period of time, taking into account its decay. Constancy test measures 
the dose calibrator’s ability to give reproducible readings daily on all available 
radioisotope windows likely to be encountered. This test should be performed daily 
using a long-lived source, usually 137Cs.  It is strongly recommended that the same 
source be readily available for use throughout the life of the calibrator. Variations in 
displayed activities must fall within ± 5% of the most recent reading at that setting 
with background and decay considered (de Farias Fragoso, 2013 and IAEA-
TECDOC, 1999).  
 
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2.4.3 Linearity of response test 
Linearity testing measures the ability of the calibrator to give the correct reading over 
the entire range of activities of its usage. The test is performed at installation and 
quarterly and using a syringe or vial of 99mTc with activity as high as the maximum 
normally prepared in radiopharmaceutical kit, in a unit dosage syringe administered 
to a patient, or in therapy, whichever is largest. In a Mo-99/Tc-99m generator this 
activity may be the total eluate in a radiopharmaceutical kit. It is recommended to 
carry out the test at installation, quarterly, after repairs and if there is displacement to 
new location (Ahmed, 2015 and Mo et al, 2006). 
Linearity test can be performed using a number of methods (i.e. decay, shielding and 
proportional methods). The decay method involves assaying a high activity of a 
short-lived radionuclide, normally 99mTc source at an initial time T0 and at pre-
determined intervals of time until activity falls below 30 μCi. The expected and 
measured activities are compared to ascertain the instrument’s linearity over the 
entire range of activities. This test also reveals the region and extent of non-linearity 
arising from saturation effects (ion-recombination); non-linearity near to zero activity 
(may indicate a wrong preset zero adjustment) and discontinuities at change of range 
(systematic error in one of the ranges). The activity measured should be within ± 5% 
of its predicted value if the instrument is working properly (IAEA TRS 454, 2006 
and IAEA-TECDOC, 1991). 
For the first calibration or reinstallation, the decay method is suitable for determining 
calibration factors to be subsequently used for the shielding method. There are 
several manufacturers of sets of lead lining that may be used for performing the 
linearity test using the shield method. The kit might have tubes of different colors 
representing different thicknesses of lead-lining. It may also have numbered and 
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lettered cylinders of different thicknesses and different linings that are used in 
combination, each having different amounts of shielding to mimic intervals of 99mTc 
decay. These sets are calibrated when first acquired by ordering a 100 mCi 99mTc 
source and performing the linearity by the decay method as well as by the shield 
method. At the beginning of the decay calibration, measurements are also made with 
the tubes. The decayed measurements are used to verify that the calibrator had a 
linear response at the time of the cylinder calibrations for period of about 72 hours 
(Ahmed, 2015 and Capintec 2004).  
If the calibrator passes that test, then the tube attenuation measurements can be used 
as a calibration for all future linearity tests. A 100 mCi source is acquired and 
measured inside each of the tubes. The measured activity of each tube relative to no 
tube should be the same as the calibrated ratios. This then confirms maintenance of a 
linear response and is completed in just a few minutes. 
The proportional method of determining the linearity response can be confirmed by 
measuring the activity of a sample and then checking the activity of carefully 
weighed portions of the sample. The minimum activity of the initial sample should 
be as large as the highest activity normally measured. The ratio of the measured 
activities should be the same as the ratio of the measured weights or volumes (i.e. 
within ±0.5% uncertainty). The weights or volumes must be measured to a degree of 
accuracy much greater than the expected linearity (Capintec, 2007 and IAEA-
TECDOC, 1991). 
 
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2.4.4 Accuracy test 
Accuracy is a measure of how close an observation is to the true value. It means that 
for given standard reference source, the indicated activity corresponds to the reading 
determined by NIST or the provider who has compared that source to one calibrated 
by the NIST. For a radionuclide calibrator, accuracy test is intended to indicate 
whether the calibrator gives correct readings over the entire energy scale (low, 
medium, and high) likely to be encountered from energy standards. Long-lived 
radionuclide sources, such as 137Cs (Energy = 662 keV) and 57Co (Energy = 122 
keV), are repeatedly assayed in the calibrator and the mean of the measurements are 
compared with the decay-corrected values within stated tolerances issued by NIST 
for that particular reference source. If the readings differ significantly (>10%) from 
the standards then the calibrator should not be used. The test should be done at 
installation, annually, and after repairs or when the instrument is moved to a new 
location within the medical facility (Powsner et al, 2013 and IAEA TRS 454, 2006). 
Zeinali et al (2008) reported eight Nuclear Medicine centres in unacceptable 
situations with regards to dose calibrator assay accuracy. The study found two 
centres within 70% uncertainty, four over 30%, one had 28%, and the other one had 
16% in terms of deviations in the measurement of the calibrated radionuclide 
standards. 
2.4.5 Geometry test 
The geometry test is intended to show that accurate measurements can be obtained 
independent of the sample geometry or size. This test is done using a syringe that is 
normally used for injection. If volumes of syringes and vials differ from the 
recommended, they must be tested throughout the range of volumes commonly used. 
The test is performed at installation and after repairs. Volume correction factor 
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(VCF) can be applied if the geometry test is within ±5% or else the calibrator must 
not be used (Powsner et al, 2013, Assan et al, 2012 and IAEA TRS 454, 2006). 
 
2.4.6 Standards relating to dose calibrators 
The International Electrotechnical Commission (IEC, 1992; 1994) and a Technical 
Report (IEC/TR 61948-4, 2006) are two standards that apply to dose calibrators. IEC 
standards are often adopted by national standards organizations. Most manufacturers 
use IEC (1992) guidelines to ensure proper equipment functioning in a standardized 
way, while IEC (1994) is intended for operators of dose calibrators. On the other 
hand, the American National Standards Institute publication ANSI N42.13 (2004) is 
also often referenced by US manufacturers. ANSI states the least requirements of 
accuracy and repeatability for dose calibrators. The recommended assay accuracy of 
a reference source (activity above 3.7MBq) in a calibrator must be within ±10% of 
the stated activity with decay correction. The reproducibility must be within ±5% of 
the mean reading for that source from a series of ten consecutive measurements with 
activity larger than 100μCi (3.7MBq) in the same geometry. See Table below for 
some limits for of acceptability for some standards for dose calibrators. Table 2.3 
shows some of the limits of acceptability for dose calibrators (Bailey et al, 2014, IEC 
TR 61948-4, 2006 and ANSI N42.13, 2004). 
 
 
 
 
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Table 2.3: Limits of acceptability for different standards for dose calibrators 
 Background Reproducibility Relative Accuracy Linearity Geometry 
(stability) response 
ANSI  ±5%  ±5%  ±10%  ±5%  ---- 
       
IAEA ±20%  ±5%   ±5%  ±5%  ±10% ±5% 
      ±2%  
NCRP ±5%  ±5%  ±5%  ±5%  
       
AAPM ±5%   ±5%   ±5%   ±5%   ---- 
 
 
2.5 SOME SOURCES OF ASSAY ERRORS 
2.5.1 User errors 
Most dose calibrator systems are user friendly if properly set up and operated as 
directed in the manufacturer’s user guide. It is important for users to understand the 
calibrator’s functionalities and characteristics. It is the duty of the licensee to ensure 
proper training is given to individuals who use the calibrator. QC tests are to be done 
as required by the manufacturer and suitable action taken if errors are outside 
recommended limits. Users of dose calibrator must understand that calibration 
numbers are unique for each radionuclide and are specific to the geometry of source. 
Therefore, dippers must be used as indicated by the manufacturer and should be 
correctly positioned in the chamber, without physical alteration or damage. Dippers 
from different companies should not be exchanged without considering the influence 
on the accuracy of the calibration coefficients (AAPM Report 181, 2012). 
 
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2.5.2 Calibration geometry  
Ideally, manufacturers of dose calibrators calibrate their systems based on the type of 
radioisotope and the sample geometry used practically. However, this may not 
always be the case since calibrations must be derived for each container type and 
specific source geometry. Therefore, calibration settings derived by the manufacturer 
can be a source of assay error since they are prone to minor fluctuations in position 
and source configurations. This means that, any variation in these parameters may 
have a bearing on the accuracy of the measurement. It is up to the operator to verify 
whether the change is insignificant (<5%) or, if significant (>10%), new dial values 
need to be determined (AAPM Report 181, 2012 and Baker et al, 2005).  
Baker et al (2005) have observed significant deviations in terms of assay accuracy 
for 99mTc isotope. The accuracy in a number of cases was better than 5%. Precisely, 
2% of the assays fell within 2% of the expected activity, 96% were within 5%, and 
only one assay was more than 10%. In this case the manufacturer’s assigned dial 
values were used. Nevertheless, the study did not reveal errors due to using geometry 
since measurements were done in the same geometry as calibrated. 
 
2.5.3 Effects of an external shield  
The external shielding of the radionuclide calibrator provided by millimeters of lead 
has several advantages. It helps in the reduction of the background effects on the 
activity measurements, reduces radiation exposure to the personnel handling the 
radioisotopes and prevents efficiency changes caused by scattering material in the 
vicinity. The manufacturer normally shields the chamber with 6 mm of lead to 
minimize external influence on the system background (Gadd et al, 2006).  
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However, the back scattering of photons and the emission of Pb K shell X-rays as a 
result of  interactions within the lead shielding will modify the calibration factors. If 
extra shielding is needed, then the calibrator must be re-calibrated or correction 
factors should be determined to ensure correct readings are obtained. It is also worth 
noting that a shield positioned around or near a calibrator improves the sensitivity of 
the ionization chamber due to backscattering of photons by the shielding. For a 
Capintec calibrator the backscattering effects are more significant for photons of 
energies between 70 keV and 250 keV than photons in other energy regions 
(Capintec 2007). 
 
2.5.4 Effects of container material 
Radioactive standard materials in the containers now being provided by NIST give a 
fair estimate of the assay of a radionuclide in a plastic or glass syringe ( wall 
thickness of 1.2 mm), even for radioisotopes with abundant low-energy photons. The 
operator should select, whenever possible, a standardized method, volume, and 
vessel for assaying radionuclides. The plastic syringe is suitable since it represents 
the delivery vehicle to the patient in most clinical conditions. Significant errors will 
occur in some instances, e.g., if the radioisotope is assayed in an appreciably 
different material and/or wall thickness than that of the standards. The vessels of 
most available standards from NIST are uniform. Plastic syringes also have a rather 
uniform wall thickness with low absorption (Capintec, 2007). 
 
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2.5.5 Effects of impurities  
The presence of radioisotope impurities affects the reading of the radionuclide dose 
calibrator, particularly in measurements of short-lived radionuclides several half-
lives after initial preparation (unless this effect is removed by photon filtration as 
with 99Mo breakthrough in 99mTc). An ionization chamber itself does not have 
intrinsic energy- discrimination ability. The existence of radioisotope impurities will 
affect the reading of the calibrator unless the effect of impurities is eliminated by 
photon filtration as is done with 99Mo breakthrough in 99mTc. However, the presence 
of low-level radionuclide impurity does not negate the effectiveness of a dose 
calibrator, if the operator is aware of its presence and has an independently 
determined calibration including photons due to the impurities (Capintec, 2007).  
2.5.6 Drift in the electronics of the calibrator 
The accuracy of the electrometer is another source of uncertainty over which the user 
may have little control. The electrometers’ inherent accuracy depends on the ability 
of the supplier to adjust the gain of the electrometer so that its measurement of 
current is traceable to primary standards. The adjustment is normally achieved by 
measuring the response of the system to a long-lived standard reference source and 
adjusting the electrometer gain until it indicates the true activity within the 
manufacturing tolerance. The gain of the system, however, will change with time and 
environment. This results from normal ageing effects of electrical components, such 
as resistors and capacitors, as well as the temperature, humidity and radiation 
exposure dependence of these components. If a reference source is supplied with the 
chamber, this allows the user of the facility to produce a benchmark reading when it 
is first supplied and to then adjust the electrometer gain if it changes with time (Gadd 
et al, 2006). 
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The electrometer linearity is another source of uncertainty. The response is regarded 
as linear if the ratio of the measured response to the true response remains constant 
over the range of current inputs for which the calibrator is designed. Electrometers 
are expected to measure currents within a deviation from provided this is contained 
within reasonable limits; it may not be a significant problem (Gadd et al, 2006). 
 
 
 
 
 
 
 
 
 
 
 
 
 
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CHAPTER THREE 
MATERIALS AND METHODS 
3.1 Introduction 
This chapter presents the materials used to accomplish the study and the methods 
involved in arriving at the results. The materials include equipment and software 
used for the study. The study is an experimental study carried out at Korle-Bu 
Teaching Hospital in Accra-Ghana. The QC tests in this work were conducted in 
accordance with well-established and accepted international standards for dose 
calibrators (AAPM Report 181, 2012, IAEA TRS 454, 2006 and IAEA-TECDOC 
602, 1991).  
3.2  MATERIALS USED FOR THIS RESEARCH 
  
 
          syringes           Forceps/tongs           gloves 
   
   Source holder/dipper                                 Vial shields         
                
Figure 3.1: Some materials used for the study 
 
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Others: Non-radioactive saline solution and 773 mCi (28.6 GBq) of 99mTc activity 
3.2.1 Materials and equipment 
Table 3.1 shows specifications for Capintec CRC®-15R and Comecer FHG LAF 
40C1F dose calibrators were used in this study.  
 
Table 3.1: Specifications for Capintec CRC-15R and Comecer dose calibrators 
Specification Capintec CRC-15R Comecer FHG LAF 40C1F 
Chamber dimensions          2  5  . 4    c  m    d  e e  p  ×  6  . 1 cm diameter 28 cm deep×7 cm diameter 
Weight 13.6 kg 4 kg 
Resolution 0.001 MBq 0.15 MBq 
Measurement range  Auto ranging from 0.001MBq Auto ranging from 
to 250 GBq 0.15MBq to 185 GBq 
Nuclide selection 9 pre-set, 4 user-defined 28 pre-set, user-defined 
radionuclide keys radionuclides keys 
Unit of display Bq or Ci Bq or Ci 
Electrometer accuracy  Better than ±2% Better than ±2% 
Response time Within 4s-16s 1s -10s 
Repeatability ±1% ±1.5% 
 
 
3.2.2 Comecer Dose Calibrator 
 One of the most prominent manufacturers of dose calibrators for use in nuclear 
medicine units is Comecer. The fully digitized detector systems in Comecer models 
give quick and dependable read-out. This enables flexible integration of this detector 
into other systems or facilities, without the need of a converter or separate read-out. 
Comecer also has unit-measurement range of up to 2 Ci for 18F used in PET systems.  
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Figure 3.2 below shows Comecer FHG LAF 40C1F calibrator in a radiochemistry 
fume hood system at Korle-Bu Teaching Hospital. 
 
Comecer display 
well chamber  
Figure 3.2: FHG LAF shielded Radiochemistry Cappa/fume hood with Comecer 
dose calibrator.  
 
3.2.3 Capintec Dose Calibrator 
well Chamber 
Electrometer 
 
Figure 3.3: Capintec CRC-15R dose calibrator  
Capintec CRC-15R dose calibrator RAMSEY, N.J 07446 made in U.S.A. P/N 7120-
2204 manufactured in 1999 by Capintec was used in this study (see Figure 3.3). It is 
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one of the most known dose calibrators because of its speed, simplicity and accuracy. 
This system takes advantage of the latest technology of auto-ranging for varying 
sample activity, giving it added speed, accuracy, and easy to use features.   
 
3.2.4 Standard radionuclide source 
 A long-lived 137Cs standard radionuclide sealed source in vial form (Code no. 
CDR562) of activity 9.21 MBq (248.92 µCi) calibrated for 13th October, 2005 and 
manufactured by AEA Technology QSA GmbH was used for constancy, relative 
response and accuracy tests.  
  
 
 137Cs Vial 
  
 
 
 
Figure 3.4: Vial containing 137Cs standard radionuclide source  
 
3.3 SOFTWARE 
3.3.1 Microsoft Excel 2010 
The data collected was analyzed using Microsoft office 2010-Excel Program under 
windows 10. Microsoft Excel is a general spreadsheet software program for sorting, 
compiling and highlighting huge quantities of data. With new features such as spark 
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lines and slicers, and improvements to Pivot Tables and other existing features, this 
version makes it easy to discover patterns or trends in the data.  
 Finally, the multi-threading feature in Microsoft Excel 2010 helps speed up data 
retrieval, sorting, and other performance enhancements. These and many other 
features made the software suitable for use in data analysis for this study. 
 
Figure 3.5: Interface for Microsoft Excel 2010 
 
3.3.2 Minitab 16 software 
Minitab is statistical software package used for all-purpose instructional application 
with easy interactive tools. Minitab was used due to its well suited capability to 
model systems making it a powerful primary tool for analyzing research data. 
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Figure 3.6: Interface for Minitab 16 software 
 
3.4 Methods 
3.4.1 Physical inspection 
This involved inspecting both radionuclide calibrators’ general condition.  
The housing and particularly surroundings of the ionization chamber were examined 
for damage. Then compatibility of power supply requirements, controls, plug-in 
modules, push-buttons and switches were also checked. Other connections were also 
inspected for availability or physical damage. The condition of remote handling 
devices, source holders, well liners and 99Mo breakthrough kits were inspected. All 
additional standard sealed sources were checked. Finally, operation and service 
manuals, and instrument log-book were located. 
3.4.2 Performance checks 
The daily performance checks on both radionuclide calibrators included auto zero, a 
background check, high voltage test and constancy checks. 
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Without the presence of any radionuclide source in the well chamber or its vicinity, 
the key for daily performance checks was selected.  Auto zero check was initiated 
and the displayed millivolt reading was recorded. The background check was 
initiated by choosing ―next test‖ from the prompt options at the finish of auto zero 
check. The minimum background activity of the system was accepted and noted. 
Auto zero and background tests make it possible to identify any eventual residual 
contamination in the well of the detector.  
 
Finally, high voltage test was initiated and the stable reading of the displayed system 
biasing voltage was noted. For battery alimented detectors, this test makes it possible 
to verify if the biasing volatge is within tolerance to avoid  the recombination 
region.These tests were done on daily basis and the mean values were compared with 
manufacturer’s specifications within their stated tolerance. Results were tabulated. 
 
3.4.3 Constancy check 
This test was done in addition to the daily auto zero, background and system tests.  A 
long-lived 137Cs standard radionuclide source in vial form (source number NK 581) 
of activity 9.21 MBq (248.92 µCi) calibrated for 13th October, 2005 and 
manufactured by AEA Technology QSA GmbH was used for this check. The 
appropriate operating conditions for data check were selected. The background at the 
137Cs setting was noted. With the aid of forceps, the check source was placed into the 
source holder and gently lowered into the well chamber of the calibrator. The reading 
was noted after 10s. 10s was chosen because it gives an optimum value of the 
response time for Capintec and Comecer dose calibrators (see Table 3.1). The net 
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result was obtained by subtracting the background from the measurement. The result 
was recorded and this procedure was repeated three times. The mean and its 
associated standard deviation were calculated. 
Relative response test was also done with the 137Cs check source assayed at the 137Cs, 
99mTc, 57Co, 131I, 67Ga, 133Xe and 201Tl radionuclide settings taking into account the 
background for each radionuclide window. The net readings were then recorded. The 
test was done once every week and the results were tabulated. 
3.4.4 Accuracy test 
The appropriate operating conditions were selected for the 137Cs standard 
radionuclide source. The background at this setting was noted. With the aid of 
forceps, the 137Cs standard radionuclide source of activity 9.21 MBq (248.92 µCi) 
was placed into the source holder and gently lowered into the well chamber of the 
calibrator. The net reading was noted after 10s.The procedure was repeated three 
times and the mean of the measured activity was compared to the decay-corrected 
activity of the check source. Accuracy was calculated using the formula; 
 
                                       
                              (     ) 
                 
 
3.4.5 Linearity test 
A 10ml vial containing 773 mCi (28.6 GBq) of 99mTc prepared from the eluate of a 
fresh generator whose molybdenum breakthrough test was 0.023 µCi/mCi was used 
for this test. The appropriate operating conditions for 99mTc radionuclide were 
selected on the calibrator and the background was noted at this setting. With the use 
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of forceps, a 10ml vial containing 99mTc source activity was placed into the source 
holder and gently lowered into the chamber well of the calibrator. The stable reading 
was recorded after 10s. The measured activity, time and date were noted. The 
activity was then assayed after 2, 6, 18, 30, 36, 40, 42, 48, 68, 74 and 94 hours 
respectively.  For each assay; the background, measured activity, date and time were 
recorded. The expected activity of 99mTc was calculated for each time elapsed and the 
results were tabulated. 
 
3.4.6 Geometry test 
The constant activity method was employed in this study. This involved the addition 
of gravimetrically determined cumulative volume (10-100%) of non-radioactive 
saline solution to a sample volume of known 99mTc activity in a vial or syringe. The 
appropriate operating conditions for 99mTc radionuclide were selected on the 
calibrator and the background was noted at this setting. To ensure reproducibility in 
the source geometry, the same source holder was used throughout the test and the 
vial/syringe placed in the center of the source holder. For Comecer dose calibrator 
the correct geometry (vial or syringe) was also chosen from the console. 
A 10 ml vial containing 1ml of 99mTc activity 56.67 mCi was placed into the sample 
holder with the aid of forceps. The vial was gently lowered into the chamber well 
and the reading was recorded after 10s. The measured activity and time was noted for 
both calibrators. The 10ml vial was removed from the chamber well and 0.5 ml of 
non-radioactive saline solution was carefully added to it using a 2 cc syringe. To help 
dilute the source volume easily and to avoid bubble formation, a bent needle was 
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inserted into the septum of the vial. The vial was then assayed in the calibrator. The 
measured activity, time and volume of saline were noted for both calibrators.  
This procedure was repeated each time increasing the volume of saline solution in 
steps of 0.5ml until the vial reached a total volume of 6 ml. This procedure was now 
repeated with 1.66 mCi and 1.81 mCi of 99mTc activity in 2cc and 5 cc syringes 
respectively. The mean of the measured activity was compared with the decay-
corrected activity for each volume and time elapsed. Volume correction factors 
(VCF) were calculated using the equation: 
 
                            
                                                                        (     ) 
                            
 
The 3mL sample volume was chosen as reference volume for the calculation of 
VCFs for the 10mL vial while the 1mL was chosen for the 2 cc and 5 cc syringes 
respectively.  
3.4.7 Contamination test 
This test was performed twice every week. This involved measuring the background 
at the 137Cs setting to check the dipper and/or well liner for any residual 
contamination at the end of a work day.  
Without the presence of any radionuclide source in the well chamber or its vicinity, 
the 137Cs window selected. The background at this setting was noted with the dipper 
(source holder) and liner in the well. The dipper was removed from the well and the 
background activity was noted. Finally, the well liner was also removed and the 
background noted. The liner was returned to the well to avoid contaminating the 
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chamber well. The amount of contamination was calculated from the differences 
between the background activities with and without liner and dipper.   
3.4.8 Other Statistical methods 
Statistical analysis was performed to clean out outliers from random data using the 
maximum minimum criterion of inclusion.  In certain instances the data was 
normalized to a value of interest (e.g. mean, true value etc.) within the specified error 
margin of standard protocols for the test. Regression analysis was performed to find 
the extent to which the dependent is influenced by independent variable. T-test was 
also used for score variations and p-value was calculated to show if there is any 
significant impact of a test. Finally results were validated and the developed model 
was also assessed practically.  
 
 
 
 
 
 
 
 
 
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CHAPTER FOUR 
RESULTS AND DISCUSSIONS 
In this chapter, the results obtained from chapter three are discussed. The results are 
categorized into quality control, performance evaluation, cross-calibration and 
validation of results. 
4.1 Quality Control  
Table 4.1: Physical inspection 
Nature of inspection Comecer system     Capintec system  
Housing/physical damage  No damages   No damages   
      
Power supply   Compatible  Compatible 
   
Remote handling devices,  Two available and in Two available and in good 
good condition condition 
 Source holders  One available, not broken Three available, one is broken 
    
Well liners Available  Available 
 
 99
  Mo breakthrough kit Available and in good Available and in good 
 condition condition 
Only 137 Standard Sealed Sources Cs standards Only 137Cs standards 
available available  
User/service manuals available    available 
   
Instrument log-book Reccords not found Reccords not found  
 
 
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As seen in Table 4.1, both calibrators were found in acceptable conditions with 
regards to physical inspection checks according to recommendations by IAEA-
TECDOC-602 (1991). However, the instrument log book could not be found for both 
systems. 
4.2  Daily quality control   
 
Table 4.2:  Daily tests on Capintec 
Test Result     Criterion Remark 
        
Auto Zero (mV) 0.049 ± 7.14%  ± 0.05 mV passed 
         
Background (µCi)          52.90 ± 7.72 µCi 27-500 µCi passed 
         
High voltage test(V)  0-0.15  155 ±15.5 V failed 
     
162.6-162.9 155 ±15.5 V passed 
      
Data Check  191.9± 2.6% ±5% or ±10% passed 
Cs-137 (µCi) 
 
With  the evaluation criterion stipulated by Capintec (2007 and 2015) operation and 
service manuals, and recommendations given in IAEA TRS 454 (2006) and IAEA-
TECDOC-602 (1991), daily performance tests for Capintec were within acceptable 
limits. However, it was observed that the high voltage test failed for five cases. This 
could have been due to an inherent inaccuracy in the electrometer leading to failure 
in registering bias voltage.  Despite the electrometer failure, all data checks with 
137Cs standard radionuclide source were found to be within the acceptable tolerance 
of ±5% indicating the presence of proper biasing voltage. This was an indication of 
drifts in the electronics of Capintec system. 
 
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Table 4.3: Daily tests on Comecer 
Test Result     Criterion Remark 
         
System Background 20.20 ± 8.61%  ±20% passed 
        
High voltage test(V) 500  500 passed 
    
Data Check  191.87 ±1.62% ±5% or  passed 
Cs-137 (µCi) ±10% 
 
With  the evaluation criterion stipulated by Comecer ( 2010)  operation and service 
manuals and the recommendations given  IAEA TRS 454 (2006) and IAEA-
TECDOC-602 (1991), it was observed that all daily performance tests on Comecer 
dose calibartor were within acceptable limits. 
 
4.3 Constancy check 
Table 4.4:  Constancy check on Comecer and Capintec systems 
137
Cs Activity (µCi) Comecer Capintec 
Measured Mean activity 185.1±1.2% 193.7±0.74% 
SD 2.2 1.4 
 
 
With the tolerance levels of ±5% recommended by IAEA TRS 454 (2006), both 
Comecer and Capintec dose calibrators were found to be within acceptable 
deviations of 1.2% and 0.74% for constancy test using 187.8 µCi of 137Cs standard 
radionuclide source. This indicated that Capintec had better reproducibility than 
Comecer in terms of assaying 137Cs standards. The mean activities of 137Cs source 
with the associated standard deviations for Comecer and Capintec over a period of 18 
weeks were found to be 185.1±2.4 µCi and 193.7±1.4 µCi respectively.  
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As also seen in Figure 4.1 (a) and (b), constancy check with 137Cs standard 
radionuclide source over the entire period shows linearity indicating that both 
systems had reproducibility within the ±5% acceptable tolerance levels as required 
by well-established international protocols (IAEA TRS 454, 2006 and IAEA-
TECDOC-602, 1991). 
Capintec Comecer
Comecer Capintec True value
196.0
194.0 1.050
192.0
190.0 1.025
188.0
1.000
186.0
184.0 0.975
182.0
180.0 0.950
0 5 10 15 20 0 5 10 15 20
Week  Week  
                                     (a)                                   (b) 
Figure 4.1: (a) Graph of activity against number of weeks for constancy check (b) 
Relative deviation against number of weeks for constancy check on Comecer and 
Capintec dose calibrators. 
 
4.4 Relative response check 
Table 4.5: Relative response to 137Cs radionuclide source 
137
Cs Activity (µCi) Comecer reading (µCi)   Capintec reading (µCi)  
Radionuclide window Mean SD Mean SD 
137Cs 6.90±1.22% 0.08 7.30±4.50% 0.30 
57Co 12.23±0.84% 0.10 21.60±5.00% 1.10 
99mTc 14.17±1.06% 0.15 29.10±5.00% 1.60 
67Ga 11.80±1.01% 0.12 24.40±2.50% 1.60 
131I 10.33±0.65% 0.07 15.30±4.00% 0.60 
201Tl 7.42±8.68% 0.64 9.10±6.10% 0.60 
49 
 
Cs-137 Activity (µCi) 
Relative deviation 
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With tolerance levels of ±5% recommended by ANSI N42.13 (2004), both systems 
were within acceptable limits for relative response to 137Cs standard radionuclide 
source at 137Cs, 57Co, 99mTc, 67Ga and 131I radionuclide settings.  
Comecer was found to have better reproducibility  as compared to Capintec  with 
regards to relative response at these radionuclide settings. However, it was observed 
that both Comecer and Capintec systems had unacceptable deviations  of 8.68% and 
6.10% at the 201Tl radionuclide setting respectively. This could have been due to a 
wrong gain setting at this radionuclide setting. 
 
Cs-137 Co-57 Tc-99m Cs-137 Co-57 Tc-99m
Ga-67 I-131 Tl-201 Ga-67 I-131 Tl-201
15
13 29
25
11 21
9 17
7 13
5 9
3 5
1 1
1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10
Days  Days  
                              (a)                                    (b) 
Figure 4.2: (a) Relative response test for Comecer and (b) Relative response test for 
Capintec   using 137Cs standard radionuclide source. 
 
Figure 4.2 (a) and (b) above show stable readings with time for both Comecer and 
Capintec with regards to relative response to 137Cs standards at the radionuclide 
settings used. This indicated that both systems have good relative response within 
acceptable tolerance levels.  
 
 
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 Cs-137 Activity (mCi) 
 Cs-137 Activity (mCi) 
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4.5 Accuracy test 
Table 4.6: Accuracy of Comecer and Capintec  
Cs-137 activity (µCi) Comecer Capintec 
   
Expected  activity  187.8 187.8 
Measured Mean activity 185.1±1.4% 193.7±3.1% 
   
 
With regards to accuracy in the measurement of  187.8 µCi of 137Cs standard 
radionuclide source over a period of 18 weeks the mean of the measured activities 
with the associated uncerntainties for Comecer and Capintec dose calibrators  were 
found to be 185.1 µCi ±1.4% and  193.7 µCi ±3.1% respectivey. As seen from the 
results for accuracy test in Table 4.6 both dose calibrators were well within the ±5% 
tolerance level recommended by IAEA TRS 454 (2006). 
 
Capintec Comecer True value Comecer Capintec True value
200 1.100
196
1.050
192
188 1.000
184 0.950
180 0.900
0 5 10 15 20 0 5 10 15 20
Week  Week  
(a) (b) 
Figure 4.3:  Measured 137(a) Cs activities against number of weeks (b) Deviations of 
measured activity about the true activity of 137Cs standard radionuclide source. 
 
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Cs-137 Activity (µCi) 
Relative Value 
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The graphs in Figure 4.3 (a) and (b) above also indicate that the accuracy in the 
measurement of 137Cs standard radionuclide source on both Comecer and Capintec 
dose calibrators were well within a ±5% tolerance. 
 
4.6  Linearity response 
Table 4.7: Linearity response for Comecer to 99mTc radionuclide source 
  Time 
Background    e  l a  psed      Net measured Expected 
Date (mCi) (hrs.) Activity(mCi) Activity(mCi) 
18-11-17 0.02 0.00 773.02± 0.00% 773.02 
18-11-17 0.02 2.15 602.56± 0.10% 603.01 
18-11-17 0.02 6.10 380.56± 0.40% 382.07 
19-11-17 0.02 18.00 97.52± 0.90% 96.63 
19-11-17 0.02 24.10 48.76± 2.10% 47.75 
19-11-17 0.02 30.15 24.40± 2.80% 23.74 
20-11-17 0.02 36.13 12.19± 2.50% 11.89 
20-11-17 0.02 40.06 7.75± 2.50% 7.56 
20-11-17 0.02 42.26 6.01± 2.60% 5.86 
20-11-17 0.02 48.69 2.88± 3.20% 2.79 
21-11-17 0.02 67.94 0.36± 16.10% 0.31 
21-11-17 0.02 74.46 0.16 ± 6.70% 0.15 
22-11-17 0.02 93.94 0.017±13.20% 0.015 
 
With tolerance levels of ±5%  recommended by IAEA (TRS 454, 2006) and ANSI 
N42.13 (2004) for linearity test, Comecer was found to have linearity response 
within acceptable limits for  99mTc  activities above 1mCi. For 99mTc below 1 mCi the 
system had unacceptable deviations and this  could have been due to its low 
measurement resolution of 4.1 µCi (Comecer, 2010).  
Comecer was found to underestimate 99mTc assays below 1 mCi by 13-16%. This 
agrees with Vargas et al (2018) who have reported significant underestimation of 
99mTc activity by 10–20% resulting from measurements using Comecer dose 
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calibrators of the type VDC-405 and VDC-404. However, the activities 
underestimated were below the useful clinical range and as such cannot be the reason 
for not using Comecer for clinical assays.  
    Table 4.8: Linearity response for Capintec to 99mTc radionuclide source 
 
Time  
Background elapsed Net measured Expected 
Date      (mCi) (hrs.) Activity(mCi) Activity(mCi) 
18-11-17 0.91 0.00 871.10±0.00% 871.10  
18-11-17 0.64 2.12 676.40±0.80% 681.90 
18-11-17 0.46 6.04 398.50±8.10% 433.50  
19-11-17 0.65 18.04 106.50±1.80% 108.4 
19-11-17 0.75 24.04 52.60±2.90% 54.19 
19-11-17 0.77 30.09 26.20±2.60% 26.90  
20-11-17 0.76 36.07 13.10±3.00% 13.50 
20-11-17 0.71 40.00 8.37±2.30% 8.57  
20-11-17 0.72 42.17 6.47±3.00% 6.67 
20-11-17 0.77 48.60 3.19±0.60% 3.17 
21-11-17 0.72 67.82 0.32±5.90% 0.34  
21-11-17 0.78 74.30 0.17±6.30% 0.16 
22-11-17 0.66 93.73 0.016±5.90% 0.017  
With the tolerance level of ±5%  recommended by IAEA (TRS 454, 2006) and ANSI 
N42.13 (2004)  for linearity test, Capintec was also found to have linearity response 
within acceptable limits for 99mTc  activities above 1 mCi.  
Despite Comecers’ better regression coeficient than Capintec, the study found 
Capintec to have better measurement resolution for activities below 1 mCi. This 
could have been due to its higher measurement resolution of  0.027 µCi as compared 
to the 4.1 µCi for Comecer system (Comecer, 2010 and Capintec, 2007).  
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  99mTc DECAY CURVES 
900
y = 747.53e-0.113x800  
Comecer
R² = 0.9996 
700 Capintec
600
500
400 y = 851.9e-0.116x 
300 R² = 0.9999 
200
100
0
0 10 20 30 40 50 60 70 80 90
Time (hrs)  
Figure 4.4: Decay curves for 99mTc activities on Capintec and Comecer  
The decay curves for 99mTc both Capintec and Comecer systems were found to be 
exponential as expected and this was an indication the laws of radioactivity (see 
Figure 4.4). As also seen in Figure 4.5, both systems showed good linearity response 
within acceptable limits with good regression coeficients.   
 
7.00
y = -0.1132x + 6.6168 Capintec
6.00
R² = 0.9996 Comecer
5.00
4.00
3.00
2.00
1.00 y = -0.1157x + 6.7475 
R² = 0.9999 
0.00
-1.00 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90
-2.00
Time (hours) 
-3.00
-4.00
-5.00  
 
Figure 4.5: Linearity Response for Capintec and Comecer dose calibrators 
on logarithmic scale. 
 
54 
 
Relative Tc-99m Activity (log Tc-99m Activity (mCi) 
scale) 
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Despite showing good linearity response, the study further revealed overestimation 
of 99mTc assays by Capintec as shown in Figure 4.6 (a) and (b).  
4.6.1 99mOverestimation of Tc assays by capintec 
35.00 35.00
30.00 30.00
25.00 25.00
20.00 20.00
15.00 15.00
10.00 10.00
5.00 5.00
0.00 0.00
5 10 15 20 25 30 35 40 45 0 200 400 600 800
Comecer Tc-99m Activity (mCi) 
 Comecer Tc-99m Activity (mCi)  
(a) (b) 
Figure 4.6: (a) % of 99mTc activity overestimated by Capintec over entire range of 
activities used and  % of 99m(b) Tc activity overestimated by Capintec over useful 
clinical range. 
 
From the results for linearity test, the difference between corresponding 99mTc assays 
with decay for Capintec and Comecer was calculated and the result was expressed as 
a percentage of the indicated activity for Comecer. This was the percentage of 99mTc 
assay overestimated by Capintec. As seen in Figure 4.6 (a) and (b) above, Capintec 
was found to overestimate 99mTc assays by 11-31%. 
These observations led to further investigation of the effects of ion recombination 
and  chamber residual contamination.  
 
 
55 
 
Capintec overestimation % 
Capintec overestimation %    
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4.6.1 Capintec electrometer inacuracy 
 
1.1
Capintec
Ideal line
1.05
1
0.95
0.9
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30
Tc-99m True activity (GBq) 
 
Figure 4.7: Drifts in Capintec electrometer readings  
 
As can be seen from Figure 4.7 above, the ratio of the measured to expected activity 
for Capintec was found to <1 for 99mTc activities above 1 mCi. This indicated drifts 
in the electrometer readings for Capintec. As seen in Table 4.2 of the results for daily 
tests, Capintec electrometer failed to register the bias voltage for some tests. This 
gave a force impression of charge losses (due to ion recombination) for Capintec. 
This could have been the reason for unusually high background readings at the 99mTc 
and 137Cs radionuclide settings for Capintec. 
According to Gadd et al (2006), for most commercial dose calibrators, the effects of 
ion recombination should be less than 1% when measuring 100 GBq of 99mTc. As 
seen in Figure 4.7, the ratio of the indicated to true activity approached 1 for 99mTc 
source activities above 22 GBq and as such any recombination could have still being 
within the 1% tolerance. 
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Measured /Expeted  
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4.6.2 Effects liner and/or dipper residual contamination 
 
Dipper+liner liner only without dipper+liner
500
400
300
200
100
0
1 2 3 4 5 6 7 8 9 10
No. of  weeks 
 
Figure 4.8: Effects of residual contamination for Capintec 
 Figure 4.8 above indicates that the background readings did not differ significantly 
with presence of liner and/or dipper. The mean of background readings with their 
associated standard deviations for dipper+liner, liner only and without dipper+liner 
configurations for Capintec at the 137Cs setting were found to be 419.0±26.4 µCi, 
420.0±26.6 µCi and 419.0±23.4 µCi respectively.  
The dipper and liner contamination levels were calculated for each week and the 
results are shown in Figure 4.9 below. 
57 
 
Activity(µCi) 
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Dipper Liner
9
8
7
6
5
4
3
2
1
0
0 2 4 6 8 10
Weeks 
 
Figure 4.9: Dipper and liner contamination levels for Capintec 
 
The liner and dipper were found to have contamination levels of 1-8µ Ci and 1-3 µCi 
respectively. However, these results were below Capintec acceptable background 
range (27-500 µCi) which indicated that residual contamination was not the reason 
for the usually high background at the 137Cs and 99mTc radionuclide settings. The 
study also found non-linearity in the electronics of Capintec since the ratio of the 
measured response to the true response was not constant over the range of current 
inputs for calibrator which could have arisen from the electrometer’s inherent 
inaccuracy. This could have led to a wrong gain at the 137Cs and 99mTc radionuclide 
setting which gave a high background reading.  
 
 
 
58 
 
Activity (µCi) 
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4.7 Geometry test 
Table 4.9:  Geometry dependence for Comecer and Capintec dose calibrators 
Comecer  Activity (mCi) 10ml vial 5ml syringe 2ml syringe 
         
Mean Meaured 54.90±0.44%  1.76±1.68% 1.64±0.36% 
          
 Expected          54.66 1.79 1.65 
 
Capintec Mean Meaured  54.98±0.51% 1.71±1.16% 1.71±0.35% 
          
Expected          54.70 1.73 1.72 
 
Table 4.9 above shows the deviation of the measured from expected (decay-
corrected) activities of 99mTc activity using different sample geometries. With 
regards to geometry dependence on Comecer the uncertainties introduced by the 
10mL vial, 5mL and 2mL syringe geometry were found to be 0.44%, 1.68% and 
0.36% indicating that the results were within tolerance levels. 
 
 Similarly, the influence of geometry on Capintec for the 10mL vial, 5mL and 2mL 
syringes used were found to be 0.51%, 1.16% and 0.35% respectively. Therefore, 
with the tolerance levels of ±5% recommended by well-established international 
protocols, both systems passed geometry test (IAEA TRS 454, 2006). 
59 
 
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Capintec Comecer
1.040
1.030 y = 0.0104x + 0.973 
R² = 0.9818 
1.020
1.010
1.000
0.990 y = 0.0118x + 0.9635 
R² = 0.9454 
0.980
0.970
0.960
0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6
Volume(mL)  
Figure 4.10: Volume correction factor against sample volume for Comecer and 
Capintec dose calibrators using a 10ml vial. 
 
With regards to volume correction factors (VCF) for the 10ml vial, both calibrators 
had factors within the recommended 0.95<VCF<1.05 (IAEA TRS 454, 2006).  
 
Comecer
Capintec Capintec Comecer
y = -0.1441x + 36.228 2.00
40 R² = 0.9497 
1.50
35
30 y = -0.2881x + 35.613 1.00
R² = 0.956 0.50
25
0.00
20
-0.50 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 615
10 -1.00
0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 -1.50 Volume(ml) 
Volume (ml)  -2.00  
(a) (b) 
Figure 4.11: (a) Activity against source volume for vial (b) Error due to volume of 
source in vial. 
 
60 
 
Activity (mCi) Volume Correction Factor  
% Error 
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Despite Comecer showing better geometry dependence than Capintec for the 10ml 
vial it was found to be more sensitive to source volume variations as compared to 
Capintec. 
Table 4.10: Further vial geometry test for Comecer and Capintec 
Dose calibrator Comecer Capintec 
Volume(mL) Activity(mCi) VCF  Activity(mCi) VCF 
0.5 35.56 1.024 36.22 1.014 
1.0 35.54 1.024 36.13 1.011 
1.5 35.14 1.012 36.03 1.008 
2.0 34.94 1.007 35.95 1.006 
2.5 34.71 1.000 35.83 1.003 
3.0 34.71 1.000 35.73 1.000 
3.5 34.51 0.994 35.62 0.997 
4.0 34.39 0.991 35.62 0.997 
4.5 34.37 0.990 35.53 0.994 
5.0 34.23 0.986 35.52 0.994 
5.5 34.01 0.980 35.47 0.993 
6.0 34.01 0.980 35.47 0.993 
 Mean 34.68±1.47%  35.76±0.71%  
  SD 0.51  0.26  
 
A further investigation of the influence of vial geometry on the assayed 99mTc 
activity using Comecer and Capintec was done over a period of 9minutes. Since this 
time was much shorter than the 6hrs half-life for 99mTc, the standard deviation was 
calculated to check the deviation of activity with sample volume on the two 
calibrators. The standard deviations for Comecer and Capintec were found to be 
1.47% and 0.71% respectively. This also confirmed that both systems were within 
the ±2% tolerance stipulated by the National Physical Laboratory (Gadd et al, 2006). 
 
  
61 
 
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Comecer 2ml syringe Capintec 2mL syringe
1.015
y = 0.0085x + 0.9939 
1.010 R² = 0.9414 
1.005
1.000
y = 0.0128x + 0.9861 
0.995 R² = 0.9461 
0.990
0.985
0.980
0 0.25 0.5 0.75 1 1.25 1.5 1.75 2
Volume (mL) 
 
Figure 4.12: VCF against sample volume for the 2ml syringe. 
 
Volume correction factors were also determined for both systems using the 2ml 
syringe which is normally assayed before injecting into patients.  
According to IAEA TRS 454 (2006), new volume correction factors (VCF) must be 
determined when the influence of geometry is >5%. In addition to both calibrators 
passing this test, VCFs were determined and it was revealed that both systems had 
factors within the acceptable range of 0.95<VCF<1.05 (see Figure 4.12 above).  
62 
 
Volume correction  factor 
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Comecer
1.06
5mL syringe
1.05 Capintec
1.04
1.03 5mL syringe
1.02 Comecer
1.01 2mL syringe
1.00 Capintec
0.99 2mL syringe
0.98 Capintec
0.97 10mL Vial
0.96 Comecer
0.95 10mL vial
0.94 Ideal line
0 10 20 30 40 50 60 70 80 90 100
Sample volume as % of total container volume 
 
Figure 4.13: The influence of Source container and sample volume on assayed 99mTc 
activity within 2 percent and 5 percent uncertainties. 
 
The overall influence of source container and sample volume geometry was 
investigated by normalizing each observed measurement to its true activity and 
plotting it against the sample volume as a percentage of the total container volume. 
 It was observed that for the 10ml vial and 2 ml syringe both Comecer and Capintec 
system had geometry dependence within 2%. However, for the 5ml syringe only 
Capintec was within 2% deviation while Comecer was found to be within 5% limit 
with regards to geometry dependence.  These results also showed that Capintec was 
less sensitive to container and source volume geometry variations. 
 
 
63 
 
Observed activity/True activity 
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4.8 CHOOSING REFERENCE DOSE CALIBRATOR FOR CROSS 
CALIBRATION 
The reference dose calibrator for cross-calibration was chosen based on results from 
daily performance checks, linearity, geometry and accuracy tests on Comecer and 
Capintec dose calibrators using 131I, 99mTc and 137Cs Certified radioactivity standard 
sources.  
Table 4.11: Measurement accuracy with Comecer dose calibrator 
Source Calibration date  and Expected activity Measured 
activity (mCi) (mCi)  and date activity(mCi) 
131I 14-09-17 168.00 100.00 20-09-17 105.80±0.06% 
131I 14-09-17 33.60 20.00 20-09-17 20.10±0.50% 
99mTc 28-09-17 1411.87 1071.17 26-10-17 1070.33±0.08% 
137Cs 13-10-05 0.25 0.19 26-10-17 0.20±0.05% 
 
Table 4.12: Measurement accuracy with Capintec dose calibrator 
Source Calibration date  and Expected activity(mCi) Measured 
activity(mCi) and date activity(mCi) 
99mTc 28-09-17 1412.00 1071.17 26-10-17 1198.37±11.8% 
137Cs 13-10-05 0.25 0.19 26-10-17 0.355±86.84% 
 
 
With the tolerance level of ±10% recommended by IAEA TRS 454 (2006) results for 
the measurements of 131I, 99mTc and 137Cs calibrated sources; it was observed that 
only Comecer system was well within acceptable deviation.  Capintec was found to 
have unacceptable deviations of 11.87% and 86.84% with regards to assay accuracy 
of 99mTc and 137Cs calibrated sources respectively.  This could have been due to the 
unusually high background observed at the 99mTc and 137Cs settings for Capintec.  
64 
 
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 These deviations could have also been due to drifts in the electronics for Capintec 
(electrometer’s failure to register bias voltage) or as a result of errors in the dial 
settings leading to undesired gain. Based on these observations and assay accuracy of 
131I, 99mTc and 137Cs calibrated sources, Comecer were chosen as the reference dose 
calibrator for the cross-calibration.  
 
4.8.1 137Cs Calibration factor (CF) 
 
COMECER CAPINTEC
1.100
1.050
1.000
0.950
0.900
0 20 40 60 80
No. of readings  
Figure 4.14: Normalized 137Cs activity against number of reading within 5% error 
margin. 
 
The results were normalized to the decay-corrected activity of 137Cs standard 
radionuclide source. The activity of 137Cs with Comecer was divided by that of 
Capintec to obtain a calibration factor (CF) for each measurement.  
The mean of 137Cs calibration factors with its associated standard deviation on 
Capintec with Comecer as the reference dose calibrator was found to be 0.95±0.017. 
65 
 
Measured /True activity  
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1.05
1.04
1.03
1.02
1.01
1.00
0.99
0.98
0.97
0.96
0.95
0 5 10 15 20 25 30 35 40 45 50 55
No. of readings 
 
Figure 4.15: Error due to 137Cs calibration factor. 
 
The determined calibration factor (CF) for 137Cs was used to calculate the true 
activity of Capintec using the equation; 
 
                                   
 
As seen in Figure 4.15 above the all the results obtained using the determined 
calibration factor was found to be within 5% deviation. Therefore, the CF for 137Cs 
standard radionuclide source on Capintec was found to be practically valid. 
66 
 
Relative error  
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 99m4.9 Cross-calibration curve for Tc assays on Capintec with Comecer as the 
reference dose calibrator. 
Calibration graph
Ideal line
900
800
700
600
500
y = 0.8947x + 1.6905 
400
R² = 0.9992 
300
200
100
0
0 100 200 300 400 500 600 700 800 900
CAPINTEC CRC 15R Activity (mCi) 
 
Figure 4.16:  Calibration curve for Capintec with Comecer as reference dose 
calibrator over entire range of 99mTc source activities used. 
 
A calibration curve for 99mTc assays on Capintec was obtained using Comecer as the 
reference dose calibrator. An ideal line for which both calibrators give the same 
reading for 99mTc source activity was also plotted to investigate the deviation of the 
calibration curve from the ideal case over the entire range of 99mTc activities used.  
 The calibration equation of Capintec with Comecer as the reference dose calibrator 
over the entire range (0.016-773.02 mCi) of 99mTc activities used for the study was 
found to be Capintec = 0.8947×Comecer + 1.6905 and this had a good regression 
coefficient R² = 0.9992.  
67 
 
Comecer Activity (mCi) 
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Calibration graph
Ideal line
110
100
90
80
70
60
y= 0.9037x + 0.8961 
50
R² = 0.9949 
40
30
20
10
0
0 10 20 30 40 50 60 70 80 90 100
CAPINTENC CRC 15R Activity (mCi)  
Figure 4.17:  Calibration curve for Capintec with Comecer as reference dose 
calibrator over useful clinical range of 99mTc source activities.   
 
A calibration curve was also obtained for 99mTc source activities within the useful 
clinical range. The calibration equation of Capintec using Comecer as the reference 
dose calibrator over the useful clinical range was found to be Capintec = 
0.9037×Comecer + 0.8961 with excel and Comecer = 1.69051 + 0.894665 Capintec 
with Minitab. As seen from Figure 4.16 and Figure 4.17 above, the calibration curve 
approached the ideal line for 99mTc source activities below 25mCi. The deviation of 
the calibration curve from the ideal line was therefore greater for higher 99mTc 
activities.  
 
 
 
68 
 
COMECER Activity (mCi) 
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4.9.1 9mValidation of Tc calibration curve 
 
From the summary of the regression analysis in Appendix B.2a, R2 =0.999326934 
and the P-values for the independent variable and intercept were 2.297×10-44 and 
0.039194 respectively. These indicated that there is no significant influence of 
external factors on the independent variable and the intercept for the developed 
model. Therefore the model can be used to predict Capintec activity with Comecer as 
reference dose calibrator at 95% confidence level. Practically the model was also 
validated by measuring 99mTc activities at different time intervals. The expected 
activity (predicted with Comecer) and theoretical activity (calculated with the 
calibration equation) for 99mTc assays were compared for the calibration curve 
developed with Excel and Minitab (Table 4.13 and Table 4.14). 
 
Table 4.13: Excel validation of 99mTc calibration  
Capintec Comecer Theoretical 
534.00 476.00 479.46±0.73% 
431.00 389.00 387.31±0.44% 
301.00 273.00 271.00±0.73% 
244.00 222.00 220.00±0.90% 
113.00 104.00 102.79±1.16% 
91.00 83.00 83.11±0.13% 
69.00 64.00 63.42±0.90% 
14.00 14.00 14.22±1.55% 
 
 
 
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Table 4.14: Minitab validation of 99mTc calibration  
Capintec Comecer Theoretical 
534.00 476.00 479.44±0.72% 
431.00 389.00 387.29±0.44% 
301.00 273.00 270.98±0.74 
244.00 222.00 219.99±0.91% 
113.00 104.00 102.79±1.17% 
91.00 83.00 83.11±0.13% 
69.00 64.00 63.42±0.90% 
14.00 14.00 14.22±1.54% 
 
As shown in Table 4.13 and Table 4.14, practical validation of 99mTc calibration 
using Excel and Minitab were found to be within deviations of 2% .  Therefore, the 
calibration equation or curve can be used to calculate the correct 99mTc activity of 
Capintec with Comecer as the reference dose calibrator. 
 
4.10 99m 137Determination of new dial value (NA) for Tc and Cs on Capintec 
 
Based on the unusually background reading observed at the 99mTc and 137Cs and the 
electrometers’ failure to register the correct biasing voltage (see Table 4.2), new dial 
values were determined for Capintec to adjust the gain of the electrometer so that its 
measurements could be traceable to primary standards for 99mTc and 137Cs certified 
radionuclide sources. The new dial values on Capintec were determined using a 
modified equation of the gain equation (2.3.8) given by Capintec (2007).  
 
 
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The modified equation was given by; 
          
  w                     (     )                            
     
                 
4.10.1 99mTc new dial value (NA) on Capintec 
 
Table4.15: Old and new dial value for 99mTc on Capintec 
Old NA Measured Expected   New NA   
80 676.40±12.20% 603.01 100  
80 398.50±4.30% 382.07 87 
80 106.50±10.20% 96.63 97 
80 52.60±10.20% 47.75 97 
80 26.20±10.40% 23.74 97 
80 13.10±10.20% 11.89 97 
80 8.37±10.70% 7.56 98 
80 6.47±10.40% 5.86 97 
80 0.32±3.2% 0.31 85 
80 0.016±6.70% 0.015 91 
  Mean 95 ±5 
 
As seen from Table 4.15, the dial value NA = 80 supplied by Capintec for 99mTc gave 
assay accuracy within 3.20-12.20%.  
Using equation (4.9.1), the theoretical dial value for 99mTc on Capintec was found to 
be NA = 95±5. This dial value was validated practically to determine its useful 
clinical range within the manufacturing tolerance. This involved adjusting the 
electrometer displayed dial value within the theoretical range (90-100) until the 
display indicated the true activity of 99mTc certified source within ±3% tolerance 
(Capintec 2007, 1990). 
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Table 4.16: Practical range of 99mTc dial value on Capintec 
New NA Measured Expected Measured Expected 
 94 82.0±1.0% 81.2 42.2±2.0% 41.3 
 95 82.1±0.7% 81.5 42.0±2.0% 41.3 
 96 80.8±0.5% 80.4 41.7±1.0% 42.2 
 97 80.8±0.5% 80.4 41.4±2.0% 42.3 
 98 80.9±0.7% 81.5 41.6±2.0% 42.3 
 Mean 96±2 
     
The new dial value for 99mTc on Capintec was found to be practically valid for  
NA = 96 ± 2. This gave assay accuracy within ±2%. 
Old NA New NA
13.0
11.0
9.0
7.0
5.0
3.0
1.0
-1.0
-3.0
99mTc assays 
 
Figure 4.18: Error due to old and New dial values for 99mTc assays on Capintec. 
 
With this practical dial value of NA = 96 ± 2 the uncertainty in 99mTc assays on 
Capintec was found to be within 0.5-2% as compared to the 3.20-12.20% with dial 
value NA = 80 supplied by Capintec. Therefore, with the calculated dial value the 
agreement between the calculated and observed responses for Capintec fell within 
the ±3% manufacturing tolerance as required by Capintec (Capintec 2007, 1990). 
72 
 
%Error 
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4.10.2 137 Cs dial value (NA) on Capintec 
 
The dial value for 137Cs on Capintec was also determined and practically validated. 
As shown in Table 4.17, with dial value NA = 220 supplied by Capintec for 137Cs 
assays the drift in the gain setting gave large uncertainties within 133-137%. The 
theoretically determined dial value for 137Cs was found to be NA = 628 ± 7.   
Table 4.17: New dial value for 137Cs on Capintec 
Old NA Measured Expected New NA 
220 434±133% 187 626 
220 434±133% 187 626 
220 432±132% 187 623 
220 432±132% 187 623 
220 436±134% 187 629 
220 428±129% 187 616 
220 434±133% 187 626 
220 435±133% 187 627 
220 443±137% 187 641 
220 445±138% 187 644 
220 434±133% 187 626 
220 437±134% 187 631 
220 438±135% 187 632 
220 435±133% 187 627 
  Mean 628±7 
 
This theoretically determined dial value was validated practically to determine its 
useful clinical range and the uncertainty involved by assaying a known activity of 
137Cs while adjusting the dial value within its theoretical range (621-635). 
 
 
 
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Table 4.18: Practical range of 137Cs dial value  
 New NA Measured Expected 
 620 188 ±0.5 187 
 621 188±0.5% 187 
 622 187±0.0% 187 
 623 187±0.0% 187 
 624 186±0.5% 187 
 624 186±0.5% 187 
 625 186±0.5% 187 
 626 186±0.5% 187 
 627 186±0.5% 187 
 628 186±0.5% 187 
 629 185±1.1% 187 
 630 185±1.1% 187 
 631 185±1.1% 187 
 632 184±1.6% 187 
 633 184±1.6% 187 
Mean 626±4   
 
 
The theoretically determined dial value for 99mTc on Capintec was found to be 
practically valid for NA = 626 ± 4.With this practical dial value the uncertainty in 
assay of 137Cs standard radionuclide source with Capintec was within 0.5-1.6% as 
compared to the 133-137% with dial value supplied by Capintec. 
 
 
 
 
 
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CHAPTER FIVE 
CONCLUSION AND RECOMMENDATIONS 
5.1 Conclusion 
 
Performance evaluation and cross-calibration have been done on Capintec and 
Comecer radionuclide dose calibrators. The study has revealed variations in the 
performance of both systems within recommended tolerance levels. Both systems 
passed constancy, relative response and accuracy tests using 137Cs standard 
radonuclide source within acceptable limits  stipulated by IAEA and ANSI. With 
tolerance levels recommended by IAEA for linearity response and geometry 
dependence with 99mTc source activity, both systems were also found to be within 
tolerance levels.  
However, the study revealed significant overestimation and underestimation of 99mTc 
assays by Capintec and Comecer sytems respectively. The study found drifts in the 
electronics of Capintec system to be the reason for the unusually high background 
readings at 99mTc and 137Cs radionuclide settings. However, a calibration 
curve/equation and new dial values for 99mTc and 137Cs have been determined to 
ensure effective use of the system. 
 
5.1.1 Recommendations 
Based on the results of the study, the following recommendations are being made to 
the Nuclear Medicine Department, the Nuclear Regulatory Authority and the 
Research Community: 
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5.1.2 Nuclear Medicine Department 
It is recommended that purchase of more standard radionuclide sources (133Ba and 
57Co) be done for further checks of the accuracy of the calibrators over the entire 
range of energies since only 137Cs standard radionuclide source is currently available. 
It is also recommended that an instrument log book should be introduced and 
Medical Physicists engaged to supervise the performance of daily constancy, 
quarterly linearity and annual tests to ensure optimal performance and usage of the 
dose calibrators. Due to drifts in the electronics of Capintec dose calibrator, it is 
recommended that the determined Cross-calibration curve/equation and the new dial 
values for 99mTc and 137Cs be used for Capintec system until an electronic check-up 
is done. 
5.1.3 Nuclear Regulatory Authority and Radiation Protection Institute 
There is need for the provision of proper regulatory performance standards in order 
to ensure strict adherence to quality control tests at internationally recommended 
frequencies. A Radiation Safety officer should also be actively engaged over the 
radionuclide sources and equipment. There is need for ensuring that dose calibrators 
are rigorously maintained to meet the national requirements set by the Nuclear 
Regulatory Authority. 
5.1.4 Research Community 
It is recommended that further research be undertaken to assess the performance of 
both dose calibrators with the use of other radionuclide sources such 133Ba, 57Co and 
131I. There is also need for further work on the electrometers’ inherent inaccuracy, 
linearity, range changing and the effects of ion recombination for 30 to 100 GBq of 
99mTc source activities. 
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REFERENCES 
Ahmed Yassen Ali, M., & Magdh Hassan Osman, M. (2015). Assessment of 99mTc 
Dose Calibrator Performance in Nuclear Medicine Department 
(Doctoral dissertation). University of Ghana, Ghana. 
American Association of Physicists in Medicine. (2012).The selection, use, 
calibration, and quality assurance of radionuclide calibrators used in 
Nuclear Medicine. Maryland, United States: AAPM Report TG 181. 
American National Standards Institute. (2004). Calibration and Usage of ―Dose 
Calibrator‖ Ionization Chambers for the Assay of Radionuclides, 
ANSI N42.13-2004, ANSI 
Assan, B., Addison, E. K. T., Hasford, F., & Sosu, E. (2012). Calibration and 
Effective Use of a Dose Calibrator. International Journal of Science 
and Technology, 2(6), 395-400. 
Bailey, D. L., Huum, J. L., Todd-Pokropek, A., & Aswegen, A. V. (2014). Nuclear 
Medicine physics: a Handbook for Teachers and Students. Vienna: 
International Atomic Energy Agency (IAEA). 
Baker M, Chari K, Judge SM, MacMahon TD, Stroak A. (2005) A Review of 
Commercial Radionuclide Calibrators. NPL Report DQL-RN 003, 
July 2005. Teddington, Middlesex, UK: National Physical Laboratory. 
Bergeron, D. E., Cessna, J. T., Golas, D. B., Young, R. K., & Zimmerman, B. E. 
(2014). Dose calibrator manufacturer-dependent bias in assays of 123I. 
Applied Radiation and isotopes, 90, 79-83. 
Caffari, Y., Spring, P., Bailat, C., Nedjadi, Y., & Bochud, F. (2010). Activity 
measurements of 18F and 90Y with commercial radionuclide calibrators 
for Nuclear Medicine in Switzerland. Applied Radiation and Isotopes, 
68(7), 1388-1391. 
Capintec (2007) CRC-15R: Owner's Manual. Manual No.9250-0038, Rev.Y 
Capintec (2015).CRC-25R: Owner's Manual. Manual No.9250-0122, Rev.H. 
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Cherry, S. R., Sorenson, J. A., & Phelps, M. E. (2012). Physics in Nuclear Medicine 
E-Book. Elsevier Health Sciences 
Da Cunha Oliveira, P. A. (2013). Radionuclide Calibrators Inter-comparison Studies 
in Nuclear Medicine Centers Using in-situ Prepared 99mTc Sources-
Innovative Methodology Validation 
de Farias Fragoso, M. D. C., de Albuquerque, A. M., de Oliveira, M. L., de Lima, F. 
F., Barreto, F. C. P., & de Andrade Lima, R. (2013). Comparison of 
the activity measurements in Nuclear Medicine services in the 
Brazilian northeast region. Applied Radiation and Isotopes, 82, 36-44. 
Gadd, R., Baker, M., Nijran, K. S., Owens, S., Thomson, W., Woods, M. J., & 
Zananiri, F. (2006). Measurement good practice guide no. 93: protocol 
for establishing and maintaining the calibration of medical 
radionuclide calibrators and their quality control. Teddington, 
Middlesex, UK: National Physical Laboratory. 
Gagnon, D. R., McLean, R. R., Hannan, M. T., Cupples, L. A., Hogan, M., & Kiel, 
D. P. (2010). Cross-calibration and comparison of variability in two 
bone densitometers in a research setting: the Framingham experience. 
Journal of Clinical Densitometry, 13(2), 210-218. 
IAEA – TECDOC - 602: Quality Control of Nuclear Medicine Instruments, 1991 
IAEA (2006) International atomic energy agency, quality assurance for radioactivity 
measurement in Nuclear Medicine. IAEA technical reports series 
No.454, IAEA, Vienna. 
INTERNATIONAL ELECTROTECHNICAL COMMISSION, Calibration and 
Usage of Ionization Chamber Systems for Assay of Radionuclides, 
IEC 61145:1992, IEC (1992). 
INTERNATIONAL ELECTROTECHNICAL COMMISSION, Nuclear Medicine 
Instrumentation — Routine Tests — Part 4: Radionuclide Calibrators, 
IEC/TR 61948-4:2006, IEC (2006). 
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Khan, K., Khan, G., Saleem, S., Hameed, N., Naqvi, M., & uz Zaman, M. (2016). 
Accuracy and Constancy Tests of Dose Calibrator at AKUH, Karachi: 
A Clinical Audit: ―Safety is Quality‖. PJR, 23(4). 
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Libronomia Company.  Wikibooks. 
 
Meghzifene, A., & Sgouros, G. (2013, May). IAEA support to Medical Physics in 
Nuclear Medicine. In Seminars in Nuclear Medicine (Vol. 43, No. 3, 
pp. 181-187). WB Saunders. 
Mo, L., Reinhard, M. I., Davies, J. B., Alexiev, D., & Baldock, C. (2006). 
Calibration of the Capintec CRC-712M dose calibrator for 18 F. 
Applied Radiation and Isotopes, 64(4), 485-489. 
Podgorsak, E. B. (2005). Radiation Oncology Physics. Vienna: International Atomic 
Energy Agency, 123-271. 
Powsner, R. A., Palmer, M. R., & Powsner, E. R. (2013). Essentials of Nuclear 
Medicine physics and Instrumentation. John Wiley & Sons. 
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Sokole, E. B., Płachcínska, A., Britten, A., & EANM Physics Committee. (2010). 
Acceptance testing for Nuclear Medicine instrumentation. European 
Journal of Nuclear Medicine and Molecular Imaging, 37(3), 672-681 
Wooten, A. L., Lewis, B. C., Szatkowski, D. J., Sultan, D. H., Abdin, K. I., Voller, 
T.F & Lapi, S. E. (2016). Calibration setting numbers for dose 
calibrators for the PET isotopes 52Mn, 64Cu, 76Br, 86Y, 89Zr, 124 I. 
Applied Radiation and Isotopes, 113, 89-95. 
Vargas, C. S., Pérez, S. R., Baete, K., Pommé, S., Paepen, J., Van Ammel, R., & 
Struelens, L. (2018). Intercomparison of 99mTc, 18 F and 111 In activity 
measurements with radionuclide calibrators in Belgian hospitals. 
Physica Medica, 45, 134-142. 
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Zeinali, H. Z., Alirezazadeh, N., & Atabi, F. (2008). An investigation on the 
performance of dose calibrators in Nuclear Medicine centers in Iran. 
Iran. J. Radiation. Res, 6(2), 64-69. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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APPENDIX 
APPENDIX A: PERFORMANCE EVALUATION 
Days Auto zero Background        H   i g  h    voltage Data check  
   (mV) (µCi)  test (V) Cs-137 (µCi) 
1 0.05 67.40 0.10 197.00 
2 0.04 36.90 0.15 201.00 
3 -0.05 58.30 0.00 197.00 
4 0.05 55.50 162.80 191.00 
5 0.05 56.90 0.00 191.00 
6 -0.05 59.60 162.60 189.00 
7 0.04 60.30 162.80 190.00 
8 0.05 53.50 162.80 197.00 
9 0.05 54.00 162.80 189.00 
10 0.05 44.40 162.80 183.00 
11 0.05 50.10 162.80 187.00 
12 0.05 45.40 162.90 189.00 
13 0.05 45.00 0.15 190.00 
14 0.05 56.00 162.60 191.00 
15 0.05 50.40 162.80 196.00 
Mean 0.049 ±0.0035 52.90 ±7.72   191.87 ±4.75% 
 
 
 
 
 
 
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A.1b            Daily quality control on Comecer dose calibrator 
Days       Background (µci) Data check (µCi) % Deviation 
1 19.00 185.53± -0.79 
2 20.00 187.48 0.26 
3 20.00 183.58 -1.83 
4 20.00 190.98 2.13 
5 20.00 185.53 -0.79 
6 20.00 187.48 0.26 
7 20.00 179.67 -3.92 
8 20.00 185.48 -0.81 
9 20.00 191.39 2.35 
10 25.00 183.58 -1.83 
11 19.00 185.53 -0.79 
12 20.00 185.53 -0.79 
13 20.00 183.58 -1.83 
14 20.00 185.53 -0.79 
15 20.00 189.44 1.30 
 20.20 ±8.61% 191.87±1.62%  
 
 
 
 
 
 
 
 
 
 
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A.2a             Constancy check on Comecer  
                     Cs-137 Activity(µCi) 
Week Background    R1-B         R 2-B R3-B  R  ave 
1 11.6 186.0 183.5 181.6 183.7 
 
2 13.8 188.0 179.7 187.5 185.1 
3 11.6 186.2 185.5 185.5 185.7  
4 9.7 186.1 179.7 185.5 183.7 
5 13.8 190.0 189.4 183.6 187.7  
6 13.8 188.2 183.6 181.6 184.4  
7 11.6 182.3 181.6 189.6 184.4 
8 13.8 186.1 181.6 179.7 182.4  
9 11.6 184.2 189.4 181.6 185.0  
10 13.7 183.3 183.6 181.6 182.7 
11 23.4 197.0 187.5 181.6 188.7  
12 17.6 199.0 181.6 187.5 189.4  
13 13.7 188.1 181.6 181.7 183.8 
14 7.8 191.0 185.5 185.5 187.4  
15 7.8 192.0 185.5 183.5 187.0 
 
16 19.5 177.2 183.6 181.6 180.7 
17 21.5 182.1 185.5 187.5 185.0  
18 9.7 189.0 183.6 183.6 185.4 
      Mean     185.1±1.2%  
     SD          2.2 
 
 
 
  
 
 
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A.2b               Constancy check Capintec 
                                   Cs-137 Activity( µCi) 
Week Background (B)       R1-B           R2-B           R3-B  Rave 
1 457.0 199.0 190.0 197.0 195.3 
2 381.0 197.0 189.0 198.0 194.7 
3 419.0 189.0 190.0 197.0 192.0 
4 522.0 192.0 191.0 198.0 193.7 
5 565.0 192.0 190.0 197.0 193.0 
6 568.0 197.0 191.0 199.0 195.7 
7 481.0 186.0 191.0 197.0 191.3 
8 435.0 200.0 190.0 197.0 195.7 
9 522.0 192.0 190.0 198.0 193.3 
10 378.0 198.0 190.0 197.0 195.0 
11 368.0 193.0 191.0 197.0 193.7 
12 412.0 197.0 191.0 197.0 195.0 
13 303.0 195.0 192.0 198.0 195.0 
14 154.0 190.0 191.0 197.0 192.7 
15 262.0 186.0 191.0 197.0 191.3 
16 292.0 186.0 192.0 199.0 192.3 
17 333.0 193.0 191.0 198.0 194.0 
18 177.0 189.0 192.0 198.0 193.0 
                      Mean             193.7±0.74 
                      SD                 1.4 
 
 
 
 
 
 
 
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A.3a                 Relative response test Capintec 
 Activity( MBq) 
   Weeks Cs-137 Co-57 Tc-99m Ga-67 I-131 Tl-201 
1 8.00 22.20 29.50 25.40 16.20 10.20 
2 7.30 19.50 26.80 22.50 14.60 9.30 
3 7.00 20.20 27.10 22.40 14.20 8.50 
4 7.10 21.70 27.10 24.40 15.00 8.70 
5 7.60 22.30 29.70 25.00 15.50 9.10 
6 7.10 22.40 30.20 25.30 15.30 8.50 
7 7.30 22.80 31.30 25.70 15.60 8.80 
8 6.90 20.70 28.30 23.60 14.80 8.90 
9 7.40 22.40 30.60 25.20 15.60 9.10 
10 7.10 21.70 29.90 24.90 15.80 9.80 
Mean 7.30 21.60 29.10 24.40 15.30 9.10 
SD 0.30 1.10 1.60 1.60   0.60 0.60 
%Error  4.50 5.10 5.50 2.50   4.00 6.10 
 
 
A.3b                   Relative response test Comecer 
Activity( MBq) 
    Weeks Cs-137 Co-57 Tc-99m Ga-67 I-131 Tl-201 
1 6.88 12.16 14.11 11.78 10.31 7.59 
2 6.95 12.28 14.39 11.89 10.42 7.66 
3 6.88 12.16 14.11 11.78 10.31 7.59 
4 6.95 12.04 13.97 11.66 10.21 7.51 
5 6.95 12.41 14.25 12.01 10.42 7.66 
6 7.02 12.28 14.39 11.89 10.42 7.66 
7 6.96 12.28 14.25 11.89 10.31 7.66 
8 6.73 12.16 14.11 11.66 10.31 7.59 
9 6.88 12.28 14.11 11.78 10.31 7.66 
10 6.81 12.28 13.97 11.66 10.31 5.59 
Mean 6.90 12.23 14.17 11.80 10.33 7.42 
SD 0.08 0.10 0.15 0.12 0.07 0.64 
%Deviation  1.22 0.84 1.06 1.01 0.65 8.68 
 
 
 
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A.4a                                        Accuracy test Comecer   
                                                Cs-137 Activity (µCi) 
Week Background B   R1-B  R2-B        R3-B   Rave Expected  
1 11.6 186.0 183.5 181.6 183.7 189.0 
2 13.8 188.0 179.7 187.5 185.1 189.0 
3 11.6 186.0 185.5 185.5 185.7 189.0 
4 9.7 186.0 179.7 185.5 183.7 189.0 
4 13.8 190.0 189.4 183.6 187.7 189.0 
6 13.8 188.0 183.6 181.6 184.4 189.0 
7 11.6 182.0 181.6 189.6 184.4 189.0 
8 13.8 186.0 181.6 179.7 182.4 189.0 
9 11.6 184.0 189.4 181.6 185.0 189.0 
10 13.7 183.0 183.6 181.6 182.7 189.0 
11 23.4 197.0 187.5 181.6 188.7 189.0 
12 17.6 199.0 181.6 187.5 189.4 186.0 
13 13.7 188.0 181.6 181.7 183.8 186.0 
14 7.8 191.0 185.5 185.5 187.4 186.0 
15 7.8 192.0 185.5 183.5 187.0 186.0 
16 19.5 177.0 183.6 181.6 180.7 186.0 
17 21.5 182.0 185.5 187.5 185.0 186.0 
18 9.7 189.0 183.6 183.6 185.4 186.0 
    Mean 185.1±1.4% 187.8 
 
 
 
 
 
 
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A.4b                   Accuracy test Capintec 
                               Cs-137 Activity (µCi) 
Week Background B R1-B R2-B R3-B Rave Expected  
1 457.0 199.0 190.0 197.0 195.3 189.0 
2 381.0 197.0 189.0 198.0 194.7 189.0 
3 419.0 189.0 190.0 197.0 192.0 189.0 
4 522.0 192.0 191.0 198.0 193.7 189.0 
5 565.0 192.0 190.0 197.0 193.0 189.0 
6 568.0 197.0 191.0 199.0 195.7 189.0 
7 481.0 186.0 191.0 197.0 191.3 189.0 
8 435.0 200.0 190.0 197.0 195.7 189.0 
9 522.0 192.0 190.0 198.0 193.3 189.0 
10 378.0 198.0 190.0 197.0 195.0 189.0 
11 368.0 193.0 191.0 197.0 193.7 189.0 
12 412.0 197.0 191.0 197.0 195.0 186.0 
13 303.0 195.0 192.0 198.0 195.0 186.0 
14 154.0 190.0 191.0 197.0 192.7 186.0 
15 262.0 186.0 191.0 197.0 191.3 186.0 
16 292.0 186.0 192.0 199.0 192.3 186.0 
17 333.0 193.0 191.0 198.0 194.0 186.0 
18 177.0 189.0 192.0 198.0 193.0 186.0 
    Mean 193.7±3.1%    187.8 
 
 
 
 
 
 
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A.5a                  Linearity response test for Comecer 
Background B    Measured-B 
Date (mCi)      Time Activity(mCi) 
18-11-17 0.02 13:08 773.02 
18-11-17 0.03 15:17 602.56 
18-11-17 0.03 19:14 380.56 
19-11-17 0.02 07:11 97.52 
19-11-17 0.02 13:11 48.76 
19-11-17 0.02 19:14 24.4 
20-11-17 0.02 01:13 12.19 
20-11-17 0.02 05:09 7.75 
20-11-17 0.02 07:21 6.01 
20-11-17 0.02 13:47 2.88 
21-11-17 0.02 09:27 0.36 
21-11-17 0.02 16:29 0.19 
22-11-17 0.02 11:31 0.017 
 
 
 
A.5b              Linearity response test for Capintec 
    Measured-B 
Date Background(mCi) Time Activity(mCi) 
18-11-17 0.91 13:10 871.1 
18-11-17 0.64 15:20 676.4 
18-11-17 0.46 19:16 298 
19-11-17 0.65 07:14 106.5 
19-11-17 0.75 13:15 52.6 
19-11-17 0.77 19:16 26.2 
20-11-17 0.76 01:16 13.1 
20-11-17 0.71 05:11 8.37 
20-11-17 0.72 07:24 6.47 
20-11-17 0.77 13:49 3.09 
21-11-17 0.72 09:27 0.31 
21-11-17 0.78 16:00 0.173 
22-11-17 0.66 11:33 0.016 
 
 
 
 
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A.5c              Contamination test for Capintec 
Background activity at Cs-137 setting 
(µCi) 
Weeks         With Dipper+liner liner only     without dipper+liner 
1 394.0 402.0 410.0 
2 416.0 414.0 417.0 
3 418.0 418.0 416.0 
4 414.0 416.0 413.0 
5 409.0 410.0 408.0 
6 405.0 406.0 404.0 
7 400.0 402.0 403.0 
8 399.0 397.0 397.0 
9 452.0 455.0 449.0.0 
10 478.0 480.0 472.0 
Mean 419.0±6.3% 420.0±6.3% 419.0±5.6% 
SD 26.4 26.6 23.4 
 
 
 A.6a              2ml Syringe geometry dependence on Comecer 
Measured Expected 
Volume(mL)   Time Activity(mCi) Activity(mCi) VCF 
0.0 14:35 1.66 1.66 0.994 
0.5 14:37 1.65 1.66 1.000 
1.0 14:39 1.64 1.65 1.006 
1.5 14:41 1.64 1.64 1.006 
2.0 14:43 1.63 1.64 1.012 
Mean 1.64±0.36% 1.65 
   
 
 
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A.6b               2ml Syringe geometry dependence on Capintec 
Measured Expected 
Volume(mL)   Time Activity(mCi) Activity(mCi) VCF 
0.0 14:36 1.73 1.73 0.988 
0.5 14:37 1.73 1.73 0.988 
1.0 14:40 1.71 1.72 1.000 
1.5 14:42 1.70 1.71 1.006 
2.0 14:44 1.69 1.70 1.012 
Mean 1.71±0.35% 1.72 
   
 
 
 
 
 
 
 
 
 
 
 
 
 
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APPENDIX B: CROSS-CALIBRATION 
B.1                      Data for  Cs-137 Cross-calibration factor  
 Comecer Capintec Comecer/Capintec 
Activity-B Activity-B 
    (µCi) (µCi) 
1 185.53 194 0.96 
2 187.48 195 0.96 
3 183.58 194 0.95 
4 190.98 195 0.98 
5 185.53 195 0.95 
6 187.48 194 0.97 
7 179.67 196 0.92 
8 185.48 195 0.95 
9 183.58 195 0.94 
10 181.62 195 0.93 
11 185.53 194 0.96 
12 179.67 195 0.92 
13 183.58 196 0.94 
14 185.53 195 0.95 
15 187.48 196 0.96 
16 190.48 197 0.97 
17 185.53 196 0.95 
18 183.58 196 0.94 
19 189.44 197 0.96 
20 183.58 197 0.93 
21 185.53 197 0.94 
22 189.44 197 0.96 
23 183.58 197 0.93 
24 181.62 197 0.92 
25 189.44 197 0.96 
26 183.58 197 0.93 
27 183.58 187 0.98 
28 185.53 188 0.99 
29 183.58 187 0.98 
30 185.53 189 0.98 
31 179.67 190 0.95 
32 185.53 189 0.98 
33 179.67 190 0.95 
34 181.62 189 0.96 
35 187.48 190 0.99 
36 181.62 191 0.95 
37 183.48 190 0.97 
38 185.53 191 0.97 
39 181.62 191 0.95 
40 187.48 190 0.99 
41 183.58 190 0.97 
42 186.19 190 0.98 
43 181.62 191 0.95 
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Continuation of Appendix B.1  
44 187.48 191 0.98 
45 183.58 192 0.96 
46 183.58 191 0.96  
47 181.62 191 0.95 
48 187.48 192 0.98  
49 179.67 191 0.94 
50 179.48 192 0.93 
51 185.53 192 0.97   
52 185.53 191 0.97 
53 183.58 192 0.96 
54 181.62 191 0.95 
55 189.62 192 0.99 
56 179.67 191 0.94 
57 181.62 191 0.95 
58 181.62 191 0.95 
59 181.62 192 0.95 
60 187.48 191 0.98 
61 181.67 190 0.96 
62 185.53 190 0.98 
63 183.53 190 0.97 
64 181.62 191 0.95 
65 187.48 191 0.98 
66 185.53 190 0.98 
67 185.53 191 0.97 
68 183.58 190 0.97 
69 183.58 191 0.96 
70 187.48 191 0.98 
71 185.53 191 0.97 
72 179.67 192 0.94 
73 181.62 191 0.95 
74 183.58 190 0.97 
75 185.53 190 0.98 
Mean 184.32 192 0.958 
SD 2.86 2.74 0.0176 
Error(%) 1.55 1.42 1.84 
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B.2a             Summary of model for Tc-99m calibration curve 
 
Regression Statistics 
     
Multiple R 0.99966341 
    
R Square 0.999326934 
Adjusted      
RSquare 0.999302006 
    
Standard Error 4.700308121 
Observations 29      
     
 ANOVA       
     Significance 
   df SS MS F F 
Regression 1 885658.62 885658.6225 40087.936 2.297E-44  
Residual 27 596.5082 22.09289643  
Total 28 886255.13        
 
   Standard    U pper Lower 
  Coefficients Error t Stat P-value Lower 95% 95% 95.0% 
Intercept 2.159720258 0.9964714 2.167367965 0.039194 0.1151298 4.204311 0.1151298  
CAPINTEC 
(mCi) 0.893993913 0.0044651 200.2197198 2.297E-44 0.8848324 0.903155 0.8848324 
 
  
B.2b RESIDUALS 
CAPINTEC (mCi) Line Fit  Plot 
CAPINTEC (mCi)  Residual Plot 
5 COMECER (mCi)
4 Predicted COMECER (mCi)
3 Linear (Predicted COMECER (mCi))
900
2 800
1 700
600
0 500
-1 0 50 100 150 400 y = 0.894x + 2.1597 
300
-2 R² = 1 
200
-3 100
0
-4
CAPINTEC (mCi) 0 200 400 600 800
-5 CAPINTEC (mCi) 
  
 
Normal Probability Plot 
900
800
700
600
500
400
300
200
100
0
0 20 40 60 80 100 120
Sample Percentile 
 
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COMECER (mCi) Residuals 
COMECER (mCi) 
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APPEENDIX C: 
RECOMMENDED FREQUENCY FOR DOSE CALIBRATOR QCS 
Criteria for performance checks of dose calibrators 
 
 IAEA TRS 454 (2006) 
 
 
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APPENDIX D: 
Cs-137 STANDARD RADIONUCLIDE SOURCE CERTIFICATE 
 
 
 
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