A semi-empirical model for the generation of dose distributions produced by a scanning electron beam

Abstract

There are linear accelerators (Sagittaire and Saturne accelerators produced by Compagnie Generale de Radioiogie (CGR/MeV) Corporation) which produce broad, flat electron fields by magnetically scanning the relatively narrow electron beam as it emerges from the accelerator vaccum system. A semi-empirical model, which mimics the scanning action of this type of accelerator, was developed for the generation of dose distributions in homogeneous media. The model employs the dose distributions of the scanning electron beams. These were measured with photographic film in a polystyrene phantom by turning of the magnetic scanning system. The mean deviation of calculated from measured dose distributions is about 0.2 % , a few points have deviations as large as 2–4 % inside of the 50 % isodose curve, but less than 8 % outside of the 50 % isodose curve. The model has been used to generate the electron beam library required by a modified version of a commercially-available computerized treatment-planning system. (The RAD-8 treatment planning system was purchased from the Digital Equipment Corporation. It is currently available from Electronic Music Industries (EMI), Ltd.)