The 'cutting away' of potential secondary electron tracks explains the effects of beam size and detector wall density in small-field photon dosimetry

摘要

The well-known field-size dependent overresponse in small-field photon-beam dosimetry of solidstate detectors equipped with very thin sensitive volumes, such as the PTW microDiamond, cannot be caused by the photon and electron interactions within these sensitive layers because they are only a few micrometers thick. The alternative explanation is that their overresponse is caused by the combination of two effects, the modification of the secondary electron fluence profile (i) by a field size too small to warrant lateral secondary electron equilibrium and (ii) by the density-dependent electron ranges in the structural detector materials placed in front of or backing the sensitive layer. The present study aims at the numerical demonstration and visualization of this combined mechanism.