Scatter from radiotherapy beams emerging from primary barriers: an aid to bunker design.

Charts to assist in linear accelerator bunker design have been produced using the Monte Carlo framework, Geant4. These charts assess the amount of forward scatter produced at different angles to the beam axis by concrete and steel barriers irradiated by 6 MV and 10 MV photon beams at normal incidence. These new charts complement existing charts of broad-beam transmission through walls. This is because the existing charts give no indication of the amount of scatter emerging at large angles from the beam axis, for example, towards the maze entrance.