Spatial variation of dose and energy in air for 2-6 MeV electron beams

Abstract

In large field skin treatments with electron beams, both dose and energy vary with SSD and distance from beam central axis. The author presents data on the spatial variation of electron dose and beam energy in the air volume between the collimator of the linear accelerator and the vertical treatment plane at 520 cm SSD. Electron dose is measured with a parallel plate ion chamber and energy is calculated from absorption range measurements. Decrement lines of 90, 80 and 50% of the central axis dose are drawn in a plane containing the beam axis. In three-dimensional space the decrement lines have funnel shapes.