DOSE-RATES AND ENERGY-SPECTRA IN THE MAZE OF A LINEAR-ACCELERATOR TREATMENT ROOM

When designing an entrance maze for a linear accelerator facility, it is useful to be able to estimate both the dose rate at the entrance an d, in case further shielding is necessary, the energy spectrum of the scattered photons reaching the maze entrance. This study examines the applicability of the commonly used empirical formula contained in the National Council on Radiation Protection and Measurements (NCRP) Repor t No. 51 for estimating the dose rates at the maze entrance in a typic al treatment room, and proposes an improvement allowing for the fact t hat the initial scattering event occurs most often in the patient at t he isocentre. The X-ray energy spectrum at the maze entrance is also m easured and shown to have a lower average energy than is assumed in NC RP Report No. 51.