Monte Carlo calculations of the perturbation factor pcav for various air cavities and guard ring widths in clinical electron beams

Abstract

The aim of this work was to examine the behavior of the perturbation factor pcav for various cavity dimensions and guard ring widths of parallel-plate chambers using Monte Carlo simulation. The simulations revealed a depth dependence of the perturbation factor pcav as well as an influence of the guard ring width on the fluence inside the air cavity. In contrast to the conventional view that the guard ring should prevent the in-scattering of electrons into the sensitive volume, a sufficiently wide guard ring contributes to the compensation of obliquity effect at larger depth. © 2009 Springer-Verlag.