Shielding design for a proton medical accelerator facility

Source terms and attenuation lengths for neutrons produced by 250 MeV protons on iron, copper and soft tissue, calculated with the FLUKA Monte Carlo code, were used for the shielding calculations (walls, ceilings, and floors) for the National Centre for Oncological Hadrontherapy to be built in Italy. Appropriate hypotheses on the proton current, beam loss factors, duty factors, occupancy factors and use factors of the shields were adopted. A dose equivalent limit of 1 mSv per year in the areas where the public has access and of 2 mSv per year for facility personnel were assumed. Shielding requirements vary from 1.5 m to about 4 m of ordinary concrete. The results agree with Monte Carlo simulations of the complete geometry of the facility obtained in a previous work. The access mazes to the treatment rooms were designed by the LCS Monte Carlo code by optimizing the length and section of their legs and their wall thicknesses with the dose equivalent limit of 2 mSv per year, fixed in the areas accessed by personnel. The resulting annual neutron dose equivalent at the maze mouth is 0.6 mSv.