Dose distributions in high energy electron beams: Production of broad beam distributions from narrow beam data

Abstract

In a high energy electron beam the spatial distribution of absorbed energy is dominated by multiple scattering of the electrons. The dose distribution in a broad parallel electron beam entering a uniform phantom can be resolved into a series of narrow beams overlapping one another, in each of which the scattering conditions are identical. It is therefore possible to build up a broad beam dose distribution from a knowledge of the axial and radial dose distribution in a narrow beam. Measurements have been made of such narrow beam distributions using finely collimated electron beams in the energy range 4-10 MeV, and the resulting data added by computer to give broad beam distributions which are compared with measured isodose curves.