Secondary neutron doses in a proton therapy centre: Neutron dosimetry in proton therapy

The formation of secondary high energy neutrons in proton therapy can be a concern for radiation protection of staff. In this joint intercomparative study (CERN, SCK•CEN and IBA/IRISIB/ULB) secondary neutron doses were assessed with different detectors in several positions in the Proton Therapy Centre, Essen (Germany). The ambient dose equivalent H*(10) was assessed with Berthold LB 6411, WENDI-2, Tissue Equivalent Proportional Counter (TEPC) and Bonner Spheres (BS). The personal dose equivalent Hp(10) was measured with 2 types of active detectors and with bubble detectors. Using spectral and basic angular information the reference Hp(10) was estimated. Results concerning staff exposure show H*(10) doses between 0.5 and 1 nSv/Monitoring Unit (MU) in a technical room. The LB 6411 showed an underestimation of H*(10) while WENDI-2 and TEPC showed good agreement with BS data. A large overestimation for Hp(10) was observed for the active personal dosemeters while the bubble detectors showed only a slight overestimation.