Rapid three-dimensional treatment planning: I. Ray-tracing approach to primary component dose calculations

Algorithms for fully three-dimensional divergent-beam radiotherapy treatment planning have been developed to achieve very high sampling of dose in heterogeneous (inhomogeneous density) tissue throughout an arbitrarily oriented patient volume, in clinically acceptable times of calculation. Dose is calculated at points along numerous rays which sample each beam. To display the dose distribution, the calculated dose values for each beam are interpolated onto rectilinear grids of (arbitrary) parallel planes, scaled for beam weight and finally merged with the weighted dose contributions of other beams. In this paper we describe and demonstrate the algorithm for the primary component of the three-dimensional photon dose distribution delivered to a patient.