Simulation and measurement of air generated electron contamination in radiotherapy

Monte Carlo simulations using MCNP4A and experimental work have been performed to evaluate the contribution of electrons that are produced in air from a 6 MV x-ray beam produced by a medical linear accelerator. Results show that up to 9% of applied dose is delivered to a patient's skin surface from electrons excited in the irradiated air column. For most field sizes this constitutes approximately 30% of dose delivered to this region. This study gives clinically relevant information on the origins and quantity of electrons at the skin of patients undergoing radiation therapy.