Performance Evaluation and Dose Verification of the Low Dose Rate Permanent Prostate Brachytherapy System at the Korle-Bu Teaching Hospital

Abstract

Low dose rate prostate brachytherapy equipment that is newly acquired or substantially upgraded requires acceptance testing before being put into clinical service as well as Quality control after installation and when in use. Thus, quality control tests typically are periodic repetitions, partial or full, of acceptance and commissioning tests. The ultrasound system is the most important equipment used in LDR prostate brachytherapy. The AAPM TG 128 provide a set of instructions for quality control testing of an ultrasound system with a specific focus on those tests applicable to image guidance during a prostate implant procedure. Following the AAPM TG 128 protocol and CIRS 045 brachytherapy QA phantom as well as other protocols, eight experiments were performed to evaluate the performance of the system. The overall average axial distance in the B and F columns were found to be 10.12 ± 0.1 mm and 10.10 ± 0.11 mm respectively deviating by approximately 1.2 % and 1.0 % respectively from a standard inter- target distance of 10 mm. Also the lateral distance measured along the rows 1, 2, 3 and 4 resulted in an average distance of 10.07 ± 0.06 mm along rows B4 – C4, deviating from the standard inter- target distance of 10 mm by approximately 0.07 mm or ± 0.7 %, that of B3 – D3 also was 20.01 ± 0.07, deviating from 20 mm standard inter- target distance by 0.01 mm or 0.05 %, targets along B2 – E2 recorded an average distance of 29.56 ± 0.33 mm deviating from 30 mm standard inter- target distance by approximately -0.44 mm or -1.47 % and the last which is B1 – F1 also recorded an average distance of 39.54 ± 0.38 mm deviating from 40 mm standard inter- target distance by approximately -0.46 mm or – 1.15 %. Volume measurement accuracy of the three standard volumes, 4 cm3, 9 cm3 and 20 cm3 produced average measurements of 3.97 ± 0.16 cm3, 8.86 ± 0.29 cm3 and 20.11 ± 1.04 cm3 resulting in approximate deviations of -0.75 %, -1.56 % and 0.55 % respectively. That of the physical and internal grid alignment yielded a maximum discrepancy of 2.67 ± 0.01 mm at position 6A on the template. The probe retraction test produced no discrepancies in the “clicks” and corresponding distances. Meanwhile the depth of penetration and axial and lateral resolution test at the time performing the tests were no available standard measurements for comparison. The dose verification test consisted of three tests, the calibration point test, the source strength verification and the TPS dose verification. The calibration point test indicated that distance for maximum ionization chamber sensitivity is 3cm, so seeds can be calibrated at this point. The source strength verification were within the tolerances recommended by ICRU report 38 (ICRU, 1985). The average source strength measured was 0.651450 U ± 0.001052 U deviating from the manufacturer value of 0.64989 U by 0.242 % ± 0. 164 %. The TPS dose verification test produced results with significant errors which occurred due to post irradiation development of film with time but the doses obtained by both TPS and film followed the same pattern. The outcome of the performance evaluations indicate that for patient work, the ultrasound system and prostate brachytherapy system can provide the mechanism for accurate positioning of the brachytherapy seeds facilitating reliable identification of the target volume for accurate effective treatment.

Description

Thesis (MPhil.) - University of Ghana, 2015

Keywords

Brachytherapy, Prostate, Clinical Service, Ultrasound System

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