Enhancing shielding designs in medical radiography services in Cameroon using PHITS Monte Carlo Simulations

Radiation surveys were conducted in fifty (50) X-ray imaging units in Cameroon. The aim of the study was to evaluate the X-rays shielding for the radiation protection of medical radiation workers (MRWs) and members of the public within controlled and uncontrolled areas respectively. The measurement of the instantaneous dose rate (IDR) was performed using a well calibrated digital survey meter model RADIAGEM 2000, in four dedicated zones namely control console (Z₁), adjacent rooms (Z₂), outdoor areas (Z₃), and waiting room (Z₄). The corresponding shielding design goals (P values) were estimated and their compliance rates with the National Council of Radiation Protection and Measurements (NCRP) recommended standard were evaluated. The results indicated that, the P values of the surveyed zones expressed in mSv/week ranged as follows: Z₁ (0. 009-0. 568), 〖 Z〗₂ (0. 044-0. 284), Z₃ (0. 004-1. 204), and Z₄ (0. 004-0. 045). The average P values of Z1, Z2, Z3 and Z4 were 0. 081, 0. 09, 0. 1202, and 0. 015 mSv/week respectively. Unsuitable protections were observed in Z1, Z2, Z3, and Z4 in the magnitude of 20%, 16%, 60%, and 30% respectively. Using the Monte Carlo simulations (MCS), performance of the additional shielding to the existing 10mm of stainless steel (S10) and 150mm of concrete (C150) used in nationwide medical services was investigated. Additional layer of shielding were 5mm of HDPE (HDPE5), 5mm of PVC (PVC5), 5mm of Al (Al5), and 5mm of stainless steel (S5). Special emphasis was placed on the transmission and scattering radiations through the studied shields. Simulations reveal that, the variation of effective dose behind the barrier based on concrete in the direction of the primary photon beam increases as follow: S5-C150 < Al5-C150 <PVC5-C150 < HDPE5-C150. Behind the barrier based on stainless steel, the increasing variation was in the following order: S5-S10<Al5-S10<PVC5-S10<HDPE5-S10. The additional layers HDPE5, PVC5, Al5, and S5 of shielding material to C150 approximately reduced the transmitted dose in the magnitude of 5. 8%, 8. 2%, 13. 6%, and 46. 9% respectively. With S10, the reduction was about 5. 4%, 7. 7%, 12. 85%, and 45. 56% using HDPE5, PVC5, Al5, and S5 respectively as additional layers. In conclusion, S5-C150 and S5-S10 should be considerated as the most appropriate materials to improve shielding barriers.