Shielding calculations for a 250 MeV hospital-based proton accelerator

The accelerator shields (250 MeV protons, 400 MeV/u 16O8+ ions) and treatment rooms of the Hadrontherapy Centre, a hospital-based facility under design in Italy, were determined by means of Monte Carlo calculations. The LCS and FLUKA codes were employed, together with analytical estimates carried out by making use of empirical formulas from the literature, and the results compared. In the case of 250 MeV protons a 250 cm thick concrete wall ensures and annual dose equivalent lower than 2 mSv in the environments adjacent to the accelerator room. The best ceiling thickness was found to be 200 cm for a unitary occupancy factor. The photon dose equivalent beyond the concrete shield was also estimated using the LCS code. In the case of ions the shield thickness was calculated using empirical formulas from the literature; the concrete thicknesses calculated for protons should ensure the required dose equivalent when some local shields are added. Monte Carlo calculations of the treatment room shielding were also carried out using the FLUKA code.