Occupational Radiation Protection: Assessment of Bunker Shielding in Radiotherapy Department

Intensity Modulation Radiation Treatment (IMRT) technique increases significantly head leakage and the workload is also affected compared with Conventional treatment. The equivalent dose from medical Linear Accelerator (LINAC) System must be limited to prevent occupational and public exposure to radiation. Therefore, the shielding design must be adequate. The aim of this study was to reassess the shielding of our LINAC room designed for conventional treatment if we planned to treat 30% of the patients with IMRT technique at Aristide Le Dantec hospital. We propose a method to evaluate the equivalent dose by using empirical formulas from the report 151 of the National Council of Radiation Protection (NCRP151). We estimate the transmission factor for all barriers using the wall thicknesses. Equivalent doses for all surrounded areas were calculated and compared with those found during measurement. The doses observed here are below annual dose limit for occupational and public even when IMRT technique will be used for treatment of 30% of the patients in a LINAC room entirely shielded for conventional treatment. The results show also that the shielding was overestimated by at least a factor of 2. Adequacy of secondary shielding will depend on the IMRT patient workload. For conventional facilities that are being assessed for IMRT therapy, existing primary barriers will typically prove adequate. Accurate and conservative shielding design is essential for radiation protection professionals in clinical practice.