Monte Carlo modeling and simulation of a passive treatment proton beam delivery system using a modulation wheel

As the first phase of applying the Monte Carlo technique, specifically using the GEANT4 toolkit, to clinical patient support, we modeled and simulated the beam delivery system of the proton therapy facility installed at the National Cancer Center (NCC), Korea. Thanks to the properly designed architecture of the GEANT4 toolkit to extend its application area, modeling the elements of the beam delivery system and of their dynamic behaviors was efficiently implemented. The simulation was validated over a treatment range of passive scattering mode in a water phantom by estimating the initial beam energy and by applying this information to a simulated therapeutic proton beam (termed the spread-out Bragg peak), resulting in good correlations with the measurement data.