Biological Weighting Function for RBE Specification of Neutron Therapy Beams. Intercomparison of 9 European Centres

Abstract

Microdosimetric measurements (0.5 inch TEPC, 2 µm simulated diameter) were performed in similar conditions for 14 neutron beams with energies ranging from p(4)+Be to p(65)+Be used for radiobiology and therapy. They were collected in an intercomparison programme currently carried out by the EORTC at European facilities and aimed at the comparison of the radiation quality (in terms of RBE) of a given neutron beam with a reference neutron beam. Indeed, accurate physical and biological characteristics for these beams are urgently required. The large RBE differences (up to 50%) observed between different Neutron Therapy Centres must be accurately (<±5%) taken into account for the comparison of clinical results. In order to provide a practicable solution to the existing and unsolved problem of accounting for radiation quality variations in neutron therapy, RBE against lineal energy weighting functions have been established by unfolding methods using radiobiological data and microdosimetric spectra obtained under identical conditions at the neutron beams investigated. This empirical procedure enabled the determination of the best accuracy achievable in predicting RBE variations between neutron beams using their weighted mean lineal energy.