Microdosimetry for BNCT: First measurements at different site sizes

Microdosimetric techniques are a valuable tool for beam quality monitoring in BNCT, due to their capability to distinguish different contributions to the total dose and provide physics-based quantities related to biological effectiveness of this composite radiation field. To this aim, measurements are generally performed with gas detectors simulating a tissue-equivalent site size between 0.5 and 2 μm. This work presents instead measurements for site sizes up to 10 μm, performed in the thermal neutron field produced by the accelerator-based MUNES source available at INFN-LNL. An avalanche-confinement TEPC with boron doping in the cathode walls was used. Photon and neutron dose fractions were discriminated in the measured dose-weighted distributions based on their different lineal energy range. In the neutron component two separate peaks could be distinguished for site sizes of 5 μm and greater, the origin of which was tentatively related to contributions due to protons and alpha particles. These results allow to assess the impact of increasing site diameter on the measured relative dose contributions and provide valuable reference data for biological modelling and for comparison with solid-state microdosimeters. • New microdosimetric measurements were done in the LNL thermal neutron field. • A boron-doped gas detector was used, simulating site sizes from 0.5 to 10 μm. • Gamma and neutron dose components were assessed for each site size. • The neutron component splits in two peaks for site sizes of 5 μm and greater.