Motion-induced Monte Carlo dose calculation using deformable tetrahedral meshes

The distribution patterns estimation of energy and dose in respiratory-induced organ motion represents a technical challenge for hadron therapy treatment planning. This paper focuses on the comparison between deformable tetrahedral meshes and the conventional voxel-based structures, used as computational phantoms in four-dimensional dose calculations. The movement issued from deformable image registration of CT-images is used for both representations to calculate the 4D dose distributions. An implementation of the dose computation method for tetrahedral meshes on a deformable anatomy in case of passive scattering beam line is given using the Geant4 code. Tissue tracking is implicitly performed by the fact that the meshes maintain their topology during deformations, and the dose distribution is calculated using time-dependent tetrahedral density map issued from 4D-CT scans. Our results show that dose distributions for voxel and tetrahedral meshes are in good agreement, and dose homogeneity is almost the same.