Neutron dose assessments for the shielding of the planned heavy ion cancer therapy facility in Heidelberg

A heavy ion therapy facility will be built at the Heidelberg university hospital. For a first proof of the radiation shielding planning, dose rate assessments were performed. The major component of potential radiation exposure is neutron radiation which is produced near the treatment units and near areas with losses of the primary beam. The dose rate assessments are based on two types of models. The first one uses the integral approximation of Moyer, the second one is based on Monte Carlo methods. The calculations are applied for primary carbon and proton beams with energies of 400 MeV/u and 250 MeV/u, respectively. The resulting dose rates are compared with the requirements of the German radiation protection ordinance for people occupationally exposed to ionizing radiation and the protection of the public near the hospital. From these shielding calculations recommendations are derived for an improved shielding at the target areas and for the beam transfer lines from the synchrotron to the treatment units. (orig.)