SECONDARY-ELECTRON SCATTER IN RADIOTHERAPY - IMPLICATIONS FOR TREATMENT FIELDS IN PROXIMITY TO THE LENS OF THE EYE AND THE TESTES

For external beam photon radiotherapy treatments, secondary electrons pose unique shielding problems. Dose due to these electrons can be deposited under shielding blocks and also outside of collimated beam edges. The sources of contamination electrons are many, but the dominant one is identified as the plastic accessory tray commonly used to support shielding blocks. Because these electrons only deposit dose superficially, the critical structures that have been established which are in range of them are the lens of the eye and the testes. The present work outlines a technique that involves a low atomic number absorber placed directly over either of these structures (outside of the primary beam) to provide the necessary shielding. Use of the technique will ensure that critical structures in proximity to treatment portals have the dose to them minimized as much as possible.