Monte Carlo calculations of the perturbation factor p~(cav) for various Air cavities and guard ring widths in clinical electron beams

摘要

The aim of this work was to examine the behavior of the perturbation factor P_(caV) 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 p_(cav) 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.