Output and $k_{Q_{clin},Q_{msr}}^{f_{clin},f_{msr}}$ correction factors measured and calculated in very small circular fields for microDiamond and EFD-3G detectors.
The purpose of this work was to obtain correction factors for microDiamond and EFD-3G detectors in very small (less than 5 mm) circular fields. We also investigated the impact of possible variations in microDiamond detector inner schematics on the calculated correction factors. Output factors (OFs) of 6MV beams from TrueBeam linac collimated with 1.27-40mm diameter cones were measured with EBT3 films, microDiamond and EFD-3G detectors as well as calculated using Monte Carlo (MC) methods. Based on EBT3 measurements and MC calculations correction factors were derived for these detectors. MC calculations were performed for microDiamond detector in parallel and perpendicular orientations relative to the beam axis. Furthermore, correction factors were calculated for two microDiamond detector models, differed by the presence or absence of metallic pins. OFs obtained using all methods agreed within 2.4% for fields $\geqslant$10mm. For the cones of 1.27, 2.46, and 3.77mm maximum differences were 33.1, 6.6 and 9.1%, respectively. MC and EBT3 obtained OFs agreed within 2.2% for all fields. MC calculated correction factors for microDiamond detector in fields $\geqslant$10mm ranged within 0.98-1.02. MicroDiamond detector correction factors calculated for the 1.27, 2.46 and 3.77mm fields were 1.97, 1.14 and 0.98 with detector in parallel orientation, and these factors were 1.15, 0.92 and 0.91 in perpendicular orientation. Including metallic pins in the microDiamond model had little effect on calculated correction factors. EBT3 and MC obtained correction factors agreed within 4.6% for fields of $\geqslant$3.77mm. Discrepancies up to 21% were found for 2.46mm and 1.27mm cones. In the 3.77mm field microDiamond over-responded compared to MC and EBT3 measurements. Including metallic pins into the detector model is not necessary as their presence/absence had no effect on calculated correction factors.
Publisher URL: http://arxiv.org/abs/1802.00569
DOI: arXiv:1802.00569v1
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