3D electron dose calculation using a Voxel based Monte Carlo algorithm (VMC).

A new model for calculating electron beam dose has been developed. The algorithm is based on a two- or three-dimensional geometry defined by computerized tomography (CT) images. The Monte Carlo technique was used to solve the electron transport equation. However, in contrast to conventional Monte Carlo models (EGS4) several approximations and simplifications in the description of elementary electron processes were introduced reducing in this manner the computational time by a factor of about 35 without significant loss in accuracy. The Monte Carlo computer program does not need any precalculated data. The random access memory required is about 16 Mbytes for a 128(2) X 50 matrix, depending on the resolution of the CT cube. The Voxel Monte Carlo model (VMC) was tested in comparison to calculations by EGS4 and the "Hogstrom algorithm" (MDAH) using several fictive phantoms. In all cases a good coincidence has been found between EGS4 and VMC, especially near tissue inhomogeneities, whereas the MDAH algorithm has produced dose underestimations of up to 40%.