Radiation quality of scattered photons at the maze entrance of radiotherapy rooms for photon beams of energy 0.5-30 MeV

In the present work the energy spectra of the scattered photons, coming from linear accelerators, at maze entrances have been calculated using the Monte Carlo code for neutrons and photons, MCNP. Initial energy of photons was in the range of 0.5-30 MeV to cover the linear accelerator nominal voltages from 4-30 MV. Fluence distributions of scattered photons for different gantry angles were also calculated. The calculated average energy of scattered photons was about 100 keV at the maze entrance near the control desk area. This was mainly independent of the primary beam and other factors. It agrees well with recent measurements but is considerably different to ICRP recommendations, and so raises again the question of increasing the radiation weighting factor in such areas.