Alhakeem Eyad A, AlShaikh Sami, Rosenfeld Anatoly B, Zavgorodni Sergei F
University of Victoria, British Columbia Cancer Agency-Vancouver Island Centre; Ministry of Education.
J Appl Clin Med Phys. 2015 Sep 8;16(5):142–158. doi: 10.1120/jacmp.v16i5.5589.
The purpose of this study is to compare performance of several dosimetric meth-ods in heterogeneous phantoms irradiated by 6 and 18 MV beams. Monte Carlo (MC) calculations were used, along with two versions of Acuros XB, anisotropic analytical algorithm (AAA), EBT2 film, and MOSkin dosimeters. Percent depth doses (PDD) were calculated and measured in three heterogeneous phantoms. The first two phantoms were a 30 × 30 × 30 cm3 solid-water slab that had an air-gap of 20× 2.5 × 2.35 cm3. The third phantom consisted of 30 × 30 × 5 cm3 solid water slabs, two 30 × 30 × 5 cm3 slabs of lung, and one 30 × 30 × 1 cm3 solid water slab. Acuros XB, AAA, and MC calculations were within 1% in the regions with particle equilibrium. At media interfaces and buildup regions, differences between Acuros XB and MC were in the range of +4.4% to -12.8%. MOSkin and EBT2 measurements agreed to MC calculations within ~ 2.5%, except for the first cen-timeter of buildup where differences of 4.5% were observed. AAA did not predict the backscatter dose from the high-density heterogeneity. For the third, multilayer lung phantom, 6 MV beam PDDs calculated by all TPS algorithms were within 2% of MC. 18 MV PDDs calculated by two versions of Acuros XB and AAA differed from MC by up to 2.8%, 3.2%, and 6.8%, respectively. MOSkin and EBT2 each differed from MC by up to 2.9% and 2.5% for the 6 MV, and by -3.1% and ~2% for the 18 MV beams. All dosimetric techniques, except AAA, agreed within 3% in the regions with particle equilibrium. Differences between the dosimetric techniques were larger for the 18 MV than the 6 MV beam. MOSkin and EBT2 measurements were in a better agreement with MC than Acuros XB calculations at the interfaces, and they were in a better agreement to each other than to MC. The latter is due to their thinner detection layers compared to MC voxel sizes.
本研究的目的是比较几种剂量学方法在6和18 MV射束照射非均匀体模中的性能。采用了蒙特卡罗（MC）计算方法，以及Acuros XB的两个版本、各向异性解析算法（AAA）、EBT2胶片和MOSkin剂量计。在三种非均匀体模中计算并测量了百分深度剂量（PDD）。前两个体模是一个30×30×30 cm³的固体水板，中间有一个20×2.5×2.35 cm³的气隙。第三个体模由30×30×5 cm³的固体水板、两块30×30×5 cm³的肺组织板和一块30×30×1 cm³的固体水板组成。在粒子平衡区域，Acuros XB、AAA和MC计算结果的差异在1%以内。在介质界面和积累区域，Acuros XB与MC之间的差异在+4.4%至 -12.8%范围内。MOSkin和EBT2测量结果与MC计算结果的差异在2.5%以内，但在积累的第一厘米处观察到4.5%的差异。AAA无法预测高密度非均匀性产生的反向散射剂量。对于第三个多层肺组织体模，所有治疗计划系统（TPS）算法计算的6 MV射束PDD与MC的差异在2%以内。两个版本的Acuros XB和AAA计算的18 MV PDD与MC的差异分别高达2.8%、3.2%和6.8%。对于6 MV射束，MOSkin和EBT2与MC的差异分别高达2.9%和2.5%；对于18 MV射束，差异分别为 -3.1%和2%。除AAA外，所有剂量学技术在粒子平衡区域的差异在3%以内。18 MV射束的剂量学技术之间的差异大于6 MV射束。在界面处，MOSkin和EBT2测量结果与MC的一致性比Acuros XB计算结果更好，并且它们之间的一致性比与MC的一致性更好。后者是由于与MC体素尺寸相比，它们的探测层更薄。
