Silicon-on-insulator (SOI) microdosimeters offer a promising method for routine quality assurance (QA) for hadron therapy due to their ease of operation and high spatial resolution. However, one complication which has been shown previously is that the traditional use of the mean chord length, (lCauchy), calculated using Cauchy's formula, for SOI devices in clinical carbon ion fields is not appropriate due to the strong directionality of the radiation field. In a previous study, we demonstrated that the mean path length, (lPath), which is the mean path of charged particles in the sensitive volume (SV), is a more appropriate method to obtain microdosimetric quantities and biological relevant values, namely the relative biological effectiveness (RBE) by means of the microdosimetric kinetic model. The previous work, which was limited to mono-energetic 12C ion beams typical of heavy ion therapy (HIT), is extended here to investigate the (lPath) in a pristine proton beam as well as for spread out Bragg peaks (SOBP) for both proton and carbon ion clinical beams. In addition, the angular dependence of the SOI device for a number of different SV designs is also investigated to quantify the effects which the alignment has on the (lPath). It is demonstrated that the (lPath) can be accurately estimated along the depth of a pristine or SOBP using the energy deposition spectra for both proton and 12C ion beams. This observation allows a quick and accurate estimation of the (lPath) for experimental use.
Available for download on Thursday, October 24, 2019