Simplified Monte Carlo dose calculation for therapeutic proton beams

A simplified Monte Carlo (SMC) method has been developed for dose calculation of therapeutic proton beams. It uses the depth-dose distribution in water measured by a broad proton beam to calculate the energy loss in a material easily and accurately. It employs the water-equivalent model of inhomogeneous materials. In addition, the multiple scattering effect in the materials is also calculated using the water-equivalent thickness. The accuracy of dose calculations by the SMC method is verified by comparison with dose measurements in a heterogeneous phantom. Results of the measured dose distributions agree well with calculations by the SMC method. though those determined by the dose calculation method based on the pencil beam algorithm show a large discrepancy. Therefore, the dose-calculation method by the SMC method will be useful for application to the treatment planning for proton therapy.