The use of high density metal foils to increase surface dose in low-energyclinical electron beams

Background and Purpose: This paper describes a practical method of elevatin g the surface dose of clinical electron beams in the energy range 3-12 MeV using thin high density metal foils (tin and lead) as an alternative to tis sue equivalent bolus. Because, relative to water, these materials exhibit a high scattering power to stopping power ratio, the desired dose elevation may be achieved with less energy loss than conventional bolus and consequen tly a gain in therapeutic interval. Methods: The foil thickness required to raise the surface dose to 90% off p eak. for a given electron energy, was calculated using published scattering and stopping power data. An empirical expression is derived to facilitate: calculation of foil thickness (tin or lead) to produce a given surface dos e. Results and Conclusions: Measurements were made to confirm the predictions of the derived expression and were found to be in good agreement. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.