title: A three-dimensional electron pencil-beam algorithm.
abstract: We describe the implementation of a three-dimensional electron-dose algorithm based on a Gaussian pencil-beam model. The algorithm calculates dose to an arbitrarily distributed set of points in a heterogeneous volume. Multiple non-coplanar beams can be positioned relative to the volume. The algorithm consists of three basic components: (i) the transport of a pencil-beam through a heterogeneous volume, (ii) the evaluation of the pencil-beam fluence at a given depth in the volume in the presence of irregular fields, and (iii) the matching of points in the volume receiving a significant fluence contribution from a pencil-beam at a given depth in the volume and the calculation of dose to those points. An efficient point-matching algorithm reduces the computation time to the level of conventional two-dimensional implementations. The algorithm uses an optimised subdivision for irregular fields, and accurately predicts output factors for irregular fields placed between the final collimators and the patient. We show comparisons between the new algorithm and conventional two-dimensional calculations using measurements and calculations for finite heterogeneities, irregular fields and output factors.
authors.affiliation: Department of Radiation Therapy, Harvard Medical School, Boston, MA 02115.
authors.forename: H M
authors.initials: HM
authors.lastname: Kooy
authors.forename: H
authors.initials: H
authors.lastname: Rashid
mesh_terms: D000465:Algorithms; D004583:Electrons; D008961:Models, Structural; D011829:Radiation Dosage