PHITS Monte Carlo zoning and workplace studies of medical radiographic rooms

The commissioning of a new radiological facility or practice requires a comprehensive process for shielding design and verification process. Traditionally, shielding design has relied on deterministic methods, such as those described in NCRP Report No. 147, and Monte Carlo codes, whereas verification has been performed using dosimeters and survey meters. Although deterministic methods remain the conventional approach, Monte Carlo simulations enable more detailed assessments of complex geometries and three-dimensional (3D) dose distributions. In this study, a Monte Carlo model based on the Particle and Heavy Ion Transport code System (PHITS) version 3.33 was developed to support shielding design, workplace zoning, and verification procedures in a conventional radiography room equipped with a remote-controlled examination table. Shielding parameters were determined using both deterministic and Monte Carlo methods, while experimental dosimetric measurements were performed to validate the model. The deterministic method was used to estimate barrier thicknesses, while on-site measurements yielded dose rates and actual lead sheet thicknesses. The Monte Carlo method was used to simulate ambient equivalent dose rates and weekly air kerma. The simulation results demonstrated a mean deviation of ~ 8.11% from the measured dose rates after excluding outliers associated with the CT room. This deviation falls within the range reported in the radiation protection modelling literature. The simulated values in the patient preparation room were higher due to underestimated barrier thickness in the deterministic calculations, necessitating barrier adjustments to ensure compliance with regulatory limits. The Student's t-test revealed no statistically significant difference (p > 0.05) between the measured and estimated values obtained using the deterministic and Monte Carlo methods at the remaining measurement locations. The simulated weekly air kerma values were consistent with the recommendations specified in NCRP Report No. 147. The control room and points 100 and 50 cm from the X-ray source were classified as controlled zones; all remaining locations were classified as monitored zones. The findings presented herein support the application of the PHITS Monte Carlo code as a robust tool for detailed three-dimensional (3D) dose estimation in diagnostic radiology, complementing the methodology described in the NCRP Report 147.