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 and, 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) Report No. 51 for estimating the dose rates at the maze entrance in a typical treatment room, and proposes an improvement allowing for the fact that the initial scattering event occurs most often in the patient at the isocentre. The X-ray energy spectrum at the maze entrance is also measured and shown to have a lower average energy than is assumed in NCRP Report No. 51.