Characteristics of clinical electron beams: Current and optimal

Abstract

This thesis presents the results of two investigations into the characteristics of electron beams for application in radiation therapy. The first involves modeling the interactions between the applicator of a Siemens Mevatron KD2 linear accelerator, and the accelerator's electron beam. EGS4 Monte Carlo code is used to simulate narrow beams incident on sections of applicator trimming plate edges in order to investigate the characteristics of scattering off these edges. A model for scatter from irregular apertures is developed based on a superposition of scatter kernels from edge elements. This model is found to give central‐axis depth dose and profile data consistent with measured results. The model is also used to obtain detailed information of the characteristics of particles scattered from the electron applicator. In the second investigation, optimal electron beam properties are determined by inversion of desired dose distributions using a simulated annealing optimization method. This technique is used for several regular desired dose distributions, and various intuitive results are obtained regarding the effects electron energy and angular modulation have on resulting dose distributions. The technique is also used for several complex desired dose distributions, indicating the relative influence energy and angular modulation can have on dose conformation with electrons.