Evaluation of PHITS for microdosimetry in BNCT to support radiobiological research

The aim of this paper is to validate the microdosimetric functionality of the Monte Carlo code, PHITS, and verify its use for estimating dose and RBE for radiobiological studies performed at Kyoto University Institute for Integrated Radiation and Nuclear Science (KURNS). Lineal energy spectra produced by the KUR mixed irradiation mode were measured with a tissue equivalent proportional counter (TEPC) place in free air. The Monte Carlo calculation showed a good agreement with the measured data. In the second part of the study, a realistic set-up of a typical in-vivo radiobiological experiment was simulated with PHITS and the simulation results were compared against TLD and gold foil activation measurements. The Monte Carlo simulation results and the measured data showed an agreement within 3%. The calculated RBE also showed a close value to clinically utilised values. This study shows that PHITS can be utilised to evaluate thermal neutron fluxes and gamma ray absorbed dose rates inside a tumour like medium.