Department of Electrical Engineering, Shiraz Branch, Islamic Azad University, Shiraz, Iran. Author to whom any correspondence should be addressed.
Phys Med Biol. 2018 Jul 27;63(15):155010. doi: 10.1088/1361-6560/aad0bd.
Dosimetry of proton beams is generally evaluated in liquid water, or alternatively in solid phantoms via water equivalent ratios (WER). WER is defined as the ratio of proton range in liquid water to that in a phantom of certain material. Presently, WER is not available in the literature neither for a wide range of energies nor for variety of relevant materials. Thus, the goal of this study is to provide such data through Monte Carlo simulations. WER is calculated for 10-500 MeV energies for compact bone, adipose tissue, polymethyl methacrylate (PMMA), PTFE (teflon), graphite (C), aluminum (Al), copper (Cu), titanium (Ti), and gold (Au) using MCNPX.2.70, GEANT4, and FLUKA Monte Carlo (MC) codes. The MCNPX code was considered as the reference to which other codes were compared. The mean values of WER obtained through the MCNPX simulations for Au, Cu, Ti, Al, PTFE, graphite, PMMA, bone, and adipose tissue were 8.83, 5.40, 3.18, 2.03, 1.87, 1.52, 1.13, 1.71, and 0.96, respectively, for 10-500 MeV energy range. The maximum deviations of WER values between MCNPX and GEANT4 results were about 6.85% for adipose tissue at energies <20 MeV, whereas they were about 7.74%, 7.74% between MCNPX and FLUKA, for adipose and Al, respectively. This inter-code uncertainties are mainly due to different physic models and stopping powers in each code. Comparing the results to that in the literature, the range of discrepancy was found to be 0-8% with greatest discrepancy for Au. Based on the materials evaluated, the PMMA remained the closest to water, for a non-tissue solid material, with an average WER of 1.13, for proton energy ranging 10-500 MeV.
质子束的剂量学通常在液态水中进行评估，或者通过水当量比（WER）在固体模型中进行评估。WER 定义为质子在液态水中的射程与在特定材料模型中的射程之比。目前，文献中既没有针对广泛能量范围，也没有针对各种相关材料的 WER 数据。因此，本研究的目的是通过蒙特卡罗模拟提供此类数据。使用 MCNPX.2.70、GEANT4 和 FLUKA 蒙特卡罗（MC）代码，为 10-500 MeV 能量的致密骨、脂肪组织、聚甲基丙烯酸甲酯（PMMA）、聚四氟乙烯（PTFE，特氟龙）、石墨（C）、铝（Al）、铜（Cu）、钛（Ti）和金（Au）计算了 WER。MCNPX 代码被认为是与其他代码进行比较的基准。通过 MCNPX 模拟获得的 Au、Cu、Ti、Al、PTFE、石墨、PMMA、骨和脂肪组织的 WER 平均值分别为 8.83、5.40、3.18、2.03、1.87、1.52、1.13、1.71 和 0.96，用于 10-500 MeV 能量范围。MCNPX 与 GEANT4 结果之间的 WER 值最大偏差约为 20 MeV 以下脂肪组织的 6.85%，而对于脂肪组织和 Al，MCNPX 与 FLUKA 之间的偏差约为 7.74%、7.74%。这种代码间的不确定性主要是由于每个代码中的不同物理模型和阻止能力。将结果与文献进行比较，发现差异范围在 0-8%之间，差异最大的是 Au。基于评估的材料，对于非组织固体材料，PMMA 仍然是最接近水的，其平均 WER 为 1.13，质子能量范围为 10-500 MeV。
