Improvement of three-dimensional Monte Carlo code PHITS for heavy ion therapy

The general purpose particle and heavy ion transport code, PHITS (particle and heavy-ion transport code system), was modified for improved analysis of dose distribution in carbon therapy systems. We added two new functions into PHITS, one for an energy dispersion calculation and the other for transport in an alternating current (AC) magnetic field, which enabled 3-dimensional modelling of a carbon therapy system for the first time. With this code we calculated the dose distribution in a carbon therapy system, and these results showed good agreement with experimental data. This improved version of PHITS is a valuable tool for the design of carbon therapy aperture or for the estimation of the dose distribution in treatment planning. (author)