Overview of the PHITS Code and Its Application to Medical Physics

Particle and Heavy Ion Transport code System, PHITS, is a general purpose three-dimensional Monte Carlo particle transport simulation code developed through collaboration with several institutes in Japan and Europe. To apply PHITS to medical physics, two special functions were implemented in the code: an event generator mode and a microdosimetric tally function. Utilizing these functions, a new relative-biological-effectiveness -weighted dose estimation method for charged-particle therapy was established on the basis of the double-stochastic microdosimetric kinetic model. Owing to these features, PHITS has been used for various medical applications, such as patient dose estimation for radiotherapy and computed tomography examination.