Maze design of a gantry room for proton therapy

Monte Carlo simulations with the LCS code were performed for the design of the access maze of an isocentric gantry room for proton therapy. The double distributions of secondary neutrons, produced by 250 MeV protons in the gantry structural materials and in the patient, were determined at the treatment room access for different irradiation directions. Neutron transport was simulated in a three-leg maze of various lengths. The secondary photons produced by neutrons in the maze walls were taken into account. The simulation results were fitted by analytical expressions based on the solution of the Hubbell integral for a rectangular radiation source. Some simulations were also performed with the FLUKA code for comparison. (orig.)