Analysis of the track- and dose-averaged LET and LET spectra in proton therapy using the GEANT4 Monte Carlo code
Analysis of the track- and dose-averaged LET and LET spectra in proton therapy using the GEANT4 Monte Carlo code
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DOI：
10.1118/1.4932217
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发表时间：
2015-11-01
期刊：
影响因子：
3.8
通讯作者：
Titt, Uwe
中科院分区：
文献类型：
--
作者：
Guan, Fada;Peeler, Christopher;Titt, Uwe
目的：本研究的动机是找到并消除剂量平均线性能量转移（LET）计算错误的原因，从治疗质子在小目标，如生物细胞层，使用GEANT4蒙特卡罗代码计算。此外，其目的也是提供一个建议，以选择一个适当的LET数量从GEANT4模拟相关的生物有效性的治疗proton.Methods：作者开发了一个粒子跟踪步骤为基础的策略，计算平均LET数量（轨道平均LET，LETt和剂量平均LET，LETd）使用GEANT4不同的跟踪步长限制。步长限制是指最大允许跟踪步长。作者研究了在79.7 MeV临床质子束照射的水模型中，跟踪步长限制如何影响质子的计算LETt和LETd，其中六种不同的步长限制范围为1至500 μ m。此外，作者还分析了质子每步能量沉积的详细随机能量沉积信息，包括注量谱和剂量谱。作为参考，作者还计算了平均LET，并结合Monte Carlo方法和确定性方法分析了LET谱。结果：模拟结果表明，不同LET计算方法对LET t的步长限制效应较小，但对LETd的步长限制效应显著。这是由于体模中不同深度处的注量谱和剂量谱之间每步能量沉积的差异造成的。在GEANT 4中使用Monte Carlo粒子跟踪方法可能导致在小步长限制的剂量平台区域中产生不正确的LETd计算结果。错误的LETd结果可归因于确定GEANT 4中能量沉积沿着跟踪步骤波动的算法。不正确的LETd值导致计算RBE.Conclusions的实质性差异：当GEANT4粒子跟踪方法被用来计算目标内的平均LET值与一个小的步长限制，如小于500 μ m，作者建议使用LETt的剂量平台区域和LETd周围的布拉格峰。对于较大的步进限制，即，500 μ m时，建议沿整个布拉格曲线沿着设置LETd。转变点取决于光束参数，并且可以通过确定LETd和LETt的比率的梯度变为正值的位置来找到。(C)2015年作者。所有文章内容，除非另有说明，是根据知识共享署名3.0未移植许可证许可。
Purpose: The motivation of this study was to find and eliminate the cause of errors in dose-averaged linear energy transfer (LET) calculations from therapeutic protons in small targets, such as biological cell layers, calculated using the GEANT4 Monte Carlo code. Furthermore, the purpose was also to provide a recommendation to select an appropriate LET quantity from GEANT4 simulations to correlate with biological effectiveness of therapeutic protons.Methods: The authors developed a particle tracking step based strategy to calculate the average LET quantities (track-averaged LET, LETt and dose-averaged LET, LETd) using GEANT4 for different tracking step size limits. A step size limit refers to the maximally allowable tracking step length. The authors investigated how the tracking step size limit influenced the calculated LETt and LETd of protons with six different step limits ranging from 1 to 500 mu m in a water phantom irradiated by a 79.7-MeV clinical proton beam. In addition, the authors analyzed the detailed stochastic energy deposition information including fluence spectra and dose spectra of the energy-deposition-per-step of protons. As a reference, the authors also calculated the averaged LET and analyzed the LET spectra combining the Monte Carlo method and the deterministic method. Relative biological effectiveness (RBE) calculations were performed to illustrate the impact of different LET calculation methods on the RBE-weighted dose.Results: Simulation results showed that the step limit effect was small for LETt but significant for LETd. This resulted from differences in the energy-deposition-per-step between the fluence spectra and dose spectra at different depths in the phantom. Using the Monte Carlo particle tracking method in GEANT4 can result in incorrect LETd calculation results in the dose plateau region for small step limits. The erroneous LETd results can be attributed to the algorithm to determine fluctuations in energy deposition along the tracking step in GEANT4. The incorrect LETd values lead to substantial differences in the calculated RBE.Conclusions: When the GEANT4 particle tracking method is used to calculate the average LET values within targets with a small step limit, such as smaller than 500 mu m, the authors recommend the use of LETt in the dose plateau region and LETd around the Bragg peak. For a large step limit, i.e., 500 mu m, LETd is recommended along the whole Bragg curve. The transition point depends on beam parameters and can be found by determining the location where the gradient of the ratio of LETd and LETt becomes positive. (C) 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.