Implementation of simplified stochastic microdosimetric kinetic models into PHITS for application to radiation treatment planning

Sato, Tatsuhiko   ; Hashimoto, Shintaro  ; Inaniwa, Taku*; Takada, Kenta*; Kumada, Hiroaki*

The stochastic microdosimetric kinetic (SMK) model is one of the most sophisticated and precise models used in the estimation of the relative biological effectiveness of carbon-ion radiotherapy (CRT) and boron neutron capture therapy (BNCT). Through the introduction of Taylor expansion (TE) or fast Fourier transform (FFT), we developed two simplified SMK models and implemented them into the Particle and Heavy Ion Transport code System (PHITS). This study enables the instantaneous calculation of the equieffective dose for CRT and BNCT, considering their cellular-scale dose heterogeneities. Treatment-planning systems that use the improved PHITS as a dose-calculation engine are under development.