Electron arc therapy: Physical measurement and treatment planning techniques

Abstract

An electron beam arc therapy technique has been developed for the treatment of the post-mastectomy chest wall using a clinical linear accelerator modified for are therapy. The effects on the dose distribution of primary X ray collimators, secondary cerrobend blocks attached to the accelerator accessory tray, and tertiary cerrobend casting of the treatment area on the patient's thorax have been investigated. Multiple electron energies within the same arc, variable rad per degree, and variable shaped secondary and tertiary applicators have been employed to optimize dose uniformity across the treated surface. A computerized treatment planning program has been developed to aid in visualization and optimization of dose distributions. A simple technique to estimate the width variation in the secondary collimator necessary to compensate for radial patient thickness changes in the cephalocaudad direction is described. Electron beam energies of 6 MeV, 9 MeV, 12 MeV, 15 MeV, and 18 MeV have been studied. The physical measurements needed to implement this technique are described, and a comparison of electron are therapy dose distributions with other standard treatment techniques is presented.