Electron dose calculation using multiple-scattering theory: evaluation of a new model for inhomogeneities

In this article, the fifth in a series on the calculation of electron dose using multiple-scattering theory, the predictions of a new model for dealing with localized inhomogeneities will be examined (Med. Phys. 18, 123-132, 1991). That model is in the form of a perturbation series, and for a thick half-slab configuration explicit formulas are worked out for the dose directly deposited by the primary electrons, for three reasonable cutoffs of the series. The predictions of this model with EGS4 Monte Carlo calculations for the half-slab configuration are compared, and they are found to be quite accurate in the region under the edge of the half-slab. On the other hand, the "Hogstrom algorithm," which is currently the most advanced method in routine clinical use, is found to give poor accuracy for this configuration.