Evaluation of The Structural Shielding Adequacy of Selected General X-Ray Imaging Facilities in Sierra Leone

Abstract

The purpose of this study was to assess the structural shielding of 5 selected general x-ray imaging facilities in Freetown, Sierra Leone and to propose a design which will serve as an alternative to lead lined doors thereby achieving the highest level of protection and safety. This research work is divided into two phases. The first part involves general assessment of the 5 selected general radiography facilities. From the data collected for facility FTN-CBD-01 with an estimated 132 patients week-1, the normalized workload per patient was found to be 0.7mAmin Patient -1 Rad Room (chest bucky) and 1.5mAmin Patient -1 Rad Room ( floor and other barriers). Facility FTN-04 has an estimated 90 patients week-1 and was found to have normalized workload per patient 0.5 mAmin Patient -1 Rad Room (chest bucky) and 1.1 mAmin Patient -1 Rad Room ( floor and other barriers). These calculated values were compared with the recommended NCRP. 147 values and both facility and NCRP.147 values used to calculate required barrier thickness for both primary and secondary radiation with no significant difference recorded. Workload data for facilities FTN-CBD-02, FTN-CBD-03 and FTN-05 were not available during data collection and as such, derived NCRP 147 values were used to determine barrier shielding requirement. Calculations show the existing wall thickness of the facilities provides the required attenuation to reduce exposure to as low as reasonably achievable with the exception of 2 facilities which additional shielding will be required for the control room and entrance door. The second phase involves the use of the SimpleGeo tool kit to develop a three dimensional image of the architectural plans of all the facilities considered for the study using the detailed data of the facilities collected in the first phase of the study. Semiconductor detectors were modeled before and after each area or barrier of concerned for assessment. The x-ray tube of each facility was modeled using published procedures. A Monte Carlo N Particle 6 (MCNP6) input file was generated from the computational models of SimpleGeo for simulation. The x-ray spectrum that was used for simulation was generated at 100kV using SpeckCal software. The computational simulation is to aid verification of the values obtained from the calculations in the first part. Additionally, this will also aid propose alternative design or shielding material for facilities, thereby providing a radiation protection shielding alternative other than lead. The simulation measured the doses before and after each barrier and comparison was made with the ICRP dose requirement per day (mGy) for 20 exposures per day. Simulation results show that doses received behind the primary barriers was below ICRP recommended value of 0.00274 mGy per day with the exception of the doses at the entrance door and control room of 2 facilities. Alternative shielding materials and required thickness were recommended for facilities where appropriate lead thickness is not available.