Department of Physics and Astronomy, University of Victoria, British Columbia, Victoria V8W 3P6, Canada. Department of Medical Physics, British Columbia Cancer Agency-Vancouver Island Centre, British Columbia, Victoria V8R 6V5, Canada.
Phys Med Biol. 2018 Jul 24;63(15):155002. doi: 10.1088/1361-6560/aacfb2.
The purpose of this work was to obtain [Formula: see text] 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 design schematics on the calculated [Formula: see text] factors. Output factors (OF's) of 6 MV beams from TrueBeam linac collimated with 1.27-40 mm diameter cones were measured with EBT3 films, microDiamond and EFD-3G detectors as well as calculated (in water) using Monte Carlo (MC) methods. Based on EBT3 measurements and MC calculations [Formula: see text] factors were derived for these detectors. MC calculations were performed for microDiamond detector in parallel and perpendicular orientations relative to the beam axis. Furthermore, [Formula: see text] factors were calculated for two microDiamond detector models, differing by the presence or absence of metallic pins. The measured OFs agreed within 2.4% for fields ⩾10 mm. For the cones of 1.27, 2.46, and 3.77 mm maximum differences were 17.9%, 1.8% and 9.0%, respectively. MC calculated output factors in water agreed with those obtained using EBT3 film within 2.2% for all fields. MC calculated [Formula: see text] factors for microDiamond detector in fields ⩾10 mm ranged within 0.975-1.020 for perpendicular and parallel orientations. MicroDiamond detector [Formula: see text] factors calculated for the 1.27, 2.46 and 3.77 mm fields were 1.974, 1.139 and 0.982 with detector in parallel orientation, and these factors were 1.150, 0.925 and 0.914 in perpendicular orientation. Including metallic pins in the microDiamond model had little effect on calculated [Formula: see text] factors. EBT3 and MC obtained [Formula: see text] factors agreed within 3.7% for fields of ⩾3.77 mm and within 5.9% for smaller cones. Including metallic pins in the detector model had no effect on calculated [Formula: see text] factors. Our results show that microDiamond and EFD-3G detectors can be used in very small (1.27-3.77 mm) fields once [Formula: see text] corrections determined in this work are applied. Expected uncertainty of such measurements will be in the range of 8%-2.5%.
这项工作的目的是为微型金刚石和 EFD-3G 探测器在非常小的（小于 5mm）圆形射野中获得[公式：见正文]因子。我们还研究了微型金刚石探测器设计图的可能变化对计算出的[公式：见正文]因子的影响。使用 EBT3 胶片、微型金刚石和 EFD-3G 探测器以及使用蒙特卡罗（MC）方法在水中计算，测量了 TrueBeam 直线加速器的 6MV 射束的输出因子（OF），准直器为直径为 1.27-40mm 的圆锥。基于 EBT3 测量和 MC 计算，为这些探测器导出了[公式：见正文]因子。对微型金刚石探测器相对于射束轴进行了平行和垂直方向的 MC 计算。此外，还为两种微型金刚石探测器模型计算了[公式：见正文]因子，这两种模型的区别在于是否存在金属销。在 10mm 以上的射野中，测量的 OF 误差在 2.4%以内。对于 1.27、2.46 和 3.77mm 的圆锥，最大差异分别为 17.9%、1.8%和 9.0%。在所有射野中，MC 计算的水中输出因子与使用 EBT3 胶片获得的输出因子在 2.2%以内一致。对于微型金刚石探测器在 10mm 以上的射野，垂直和平行方向的[公式：见正文]因子范围在 0.975-1.020 之间。对于 1.27、2.46 和 3.77mm 的射野，微型金刚石探测器的[公式：见正文]因子在平行方向下为 1.974、1.139 和 0.982，在垂直方向下为 1.150、0.925 和 0.914。在探测器模型中加入金属销对计算出的[公式：见正文]因子影响不大。在 3.77mm 以上的射野中，EBT3 和 MC 获得的[公式：见正文]因子误差在 3.7%以内，在较小的圆锥射野中误差在 5.9%以内。在探测器模型中加入金属销对计算出的[公式：见正文]因子没有影响。我们的结果表明，一旦应用本文确定的[公式：见正文]校正，微型金刚石和 EFD-3G 探测器就可以用于非常小的（1.27-3.77mm）射野。此类测量的预期不确定度将在 8%-2.5%范围内。
