The use of lead as a field shaping block in high energy electron beam therapy

Abstract

Reports on measurements with a 43 MeV Siemens betatron and an SHM build-up chamber to determine the amount of radiation under the block as a function of the thickness of the block and the initial beam energy. For 6 MeV electrons, it is found that 2.0 mm of lead is required to reduce the surface dose to 5%. For 9 and 12 MeV electrons, the required thicknesses are 3.4 and 5.5 mm, respectively. Blocks of these thicknesses can easily be constructed from standard lead sheet, and can either be attached to treatment cones or placed directly on the patient.