Monte Carlo modelling of a silicon strip detector for microbeam radiation therapy

Microbeam radiation therapy is an experimental technique utilising synchrotron X-rays collimated into a planar array of microbeams. Due to the complex structure of the radiation field and high dose rate, this introduces dosimetric challenges. Current dosimetric methods are inadequate in that they lack either real-time readout, or high spatial resolution. A detector system, consisting of the Silicon Multi-Strip Detector and associated readout system was developed at the University of Wollongong. This system performs online, real-time dosimetry, and is designed for placement upstream of the patient as a transmission detector. The interaction of synchrotron radiation with this detector, both in terms of perturbative effects on the beam and interactions within the detector are investigated with the Monte Carlo simulation toolkit, Geant4. The interaction percentage of the detector with the traversing beam was determined as being (1.97 ± 0.01) %. Energy deposition was found to be uniform across the depth of the detector, negating the most proximal and distal 5-μm region, a phenomenon that may be attributed to a lack of charged particle equilibrium. The effect that the detector has on a traversing beam’s macroscopic dose deposition was determined as being a mean reduction in dose of (1.44 ± 0.15) % for depths in water between 5 and 35 mm.