MONTE-CARLO SIMULATIONS OF NEUTRON-TRANSPORT IN A LINAC RADIOTHERAPY ROOM

Medical electron accelerators for cancer radiation therapy operating at energies above 8-10 MeV produce secondary neutron radiation via (gamma, n) and (e, e'n) reactions in the various materials of the gantry. The spatial distribution of the neutron flux in the treatment room can be evaluated by the Monte Carlo method. The influence of the materials constituting the bremsstrahlung target and the gantry shield on the angular and the spatial distributions of the direct component of the flux has been evaluated by the MCNP code. The effect of room geometry and composition of wall materials on the scattered component has also been investigated.