Peripheral neutron dose model verification for real IMRT cases

Introduction Peripheral doses are directly related to second cancer risk after radiotherapy. Our group developed a methodology to estimate neutron contribution to peripheral organ doses by terms of two general models, namely abdomen and head and neck [PMB-2012;57:6167–6191]. Purpose This work aims to verify the validity of these models in real treatments, in order to evaluate the need of further improvements for specific locations beside the two generic ones. Materials and methods Neutron doses were calculated in 12 representative organs from measured thermal neutron fluences with TNRD detectors at 16 points inside the phantom [MedPhys-2014;41:112105], for two high energy (15 MV) treatments (lung and prostate). Following the methodology described in [RO107:234–241], these neutron doses were estimated by terms of number of delivered MU and facility characterization. Abdomen model was used for the prostate case while both (abdomen and headn42:276–281]. Results Values generally agreed within the 30% uncertainty range established for the models and the 15% for the measurement. Abdomen model has shown to fit better for the lung. Further studies should be needed to improve generic models in some specific locations such as skin or organs close to the field-edge. Conclusion The generic model has shown to be good enough to cover frequent high-energy specific treatments as those studied here. It seems to be no need of more specific models, while some improvements have to bee done for particular points.