A Microdosimetry Application for Microbeam Radiation Therapy Dose Delivery using TOPAS

Microbeam Radiation Therapy as a cancer treatment is developing fast due to its high therapeutic effect. This work simulates the MRT setup and the multi-slit collimator used in the creation of microbeams with the aid of TOPAS. TOPAS is a Geant4-based Monte Carlo extension developed to make simulations more readily available to both research and clinical medical physicists, as well as to extend its functionality. A multi-slit collimator is modelled to produce x-ray microbeams with a width of 50 µm and a centre to centre spacing of 400 µm. The energies range from 0 to 600 keV, and they are sampled using the synchrotron-wiggler generated spectrum employed at the biomedical facility of the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. This work aims to identify the accuracy of the dose deposition curves and peak to valley dose ratios (PVDRs) obtained with TOPAS. The PVDRs decreased with depth but increased prior to phantom exit due to the absence of back scattering. The simulated results are in line with published simulated and empirical findings, which suggest that TOPAS can be satisfactorily used as a tool for the calculation of the percentage depth dose and PVDRs at the energies considered in this study.