Poster — Wed Eve—39: Using DOSRZnrc to Study the SFD Si‐Diode for Small Field Relative Dosimetry

Abstract

Purpose: The goal of this work was to study the SFD Si‐diode (IBA Dosimetry, previously Scanditronix/Wellhofer) for small field dosimetry. Methods and Materials: The EGSnrc user code DOSRZnrc was used to construct a geometrically accurate model of the detector. The active volume was modelled as pure silicon () and 6HSiC (). For field sizes between 0.5 and 5.0 cm, water tank simulations were run and validated experimentally for isocentric detector placement at depths of 1.5, 5.0 and 10.0 cm. Detector response was investigated and correction factors calculated according to Capote et al (Med. Phys. 31 2416–22) and Alfonso et al (Med. Phys. 35 5179–86). Results: The SFDSi simulated ROFs were generally higher than the experimental values yet still within the statistical uncertainty of 1.3 to 1.5%. However, for the two smallest field sizes the data was high by as much as 3.0%. The simulated ROFs revealed no such disagreement with experiment and were statistically equivalent to the measured data. Conclusion: The active volume of the SFD detector is most likely a substrate very similar to 6HSiC and should not be modelled as pure silicon, modelling the detector as a “chip in water” may be considered a reasonable approximation but does hinge on the correct choice of material for the active volume and it appears no correction factor is required for small field relative output factors measured with the SFD Si‐diode detector, however a reduction in the statistical uncertainty would be desirable.