J0102-3-2 4D Monte Carlo Dose Calculations for Particle Therapy Combined with the Spring Network Model of Lung Motion

Abstract

To enable the evaluation of the impact of respiratory motion on charged particle therapy and to realize 4D treatment planning while keeping CT exposure as low as possible, we are developing a Monte Carlo dose calculation system combined with the spring network model of lung motion. The calculated 3D shape of the lung for a given phase is transformed to a voxel data set. For each phase, assuming carbon-ion beam irradiation, biological dose distribution is calculated using the Monte Carlo particle and heavy ion transport code PHITS coupled with a microdosimetric kinetic model. The dose is mapped onto the reference data set to obtain the accumulated dose. The first version of the 4D dose calculation system we have developed so far can successfully read the data set for each phase and calculate the accumulated dose. The number of the phases to be sampled and their weights can be set arbitrarily, without need of additional CT scanning. Our results indicate that the dose distribution can significantly change with phase and that many data sets may be needed to accurately evaluate the dose to the surrounding normal tissue.