Validation of linear energy transfer computed in a Monte Carlo dose engine of a commercial treatment planning system
Validation of linear energy transfer computed in a Monte Carlo dose engine of a commercial treatment planning system
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DOI：
10.1088/1361-6560/ab5e97
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发表时间：
2020-01-01
影响因子：
3.5
通讯作者：
Both, Stefan
中科院分区：
文献类型：
--
作者：
Wagenaar, Dirk;Tran, Linh T.;Both, Stefan
质子的相对生物有效性（RBE）是高度可变的，难以量化。然而，RBE与局部电离密度相关，其可以与物理可测量的剂量加权线性能量转移（LETD）相关。本研究的目的是使用微剂量测量和独立LETD计算，验证市售治疗计划系统（TPS）中质子治疗束的LETD计算（Open-MCsquare（MCS））。TPS（RayStation v6 R）用于在CIRS-731-HN拟人化体模上生成三个解剖部位的治疗计划（脑、鼻咽、颈部），以计算LETD分布。测量在格罗宁根大学医学中心质子治疗中心（Proteus Plus，IBA）进行，使用μ（+）探针，利用绝缘体上硅微剂量计能够检测线性能量低至0.15 keV μ m（-1）的组织。剂量平均的平均线性能量的深度分布进行了测量，为70和130兆电子伏的点在水中，并为三个治疗计划在水中和一个拟人化的幻影。将测量值与TPS和MCS独立剂量计算引擎中计算的LETD进行比较。比较了D中心点与D中心点LETD的γ指数，一致距离标准为2 mm，剂量差异标准增加，以确定达到90%通过率的标准。D中心点的测量结果与TPS和MCS中计算的D中心点LETD吻合良好。在不同的D中心点LETD差异标准下，单点通过率达到90%阈值（TPS：1% MCS：1%），水中处理计划（TPS：3% MCS：6%）和拟人化体模中的治疗计划（TPS：6% MCS：我们得出结论，RayStation TPS和开放MCSquare中的D中心点LETD计算精度在6%以内，并且足以用于临床D中心点LETD评估和优化。这些发现消除了在临床实施D中心点LETD评估和优化质子治疗计划的道路上的一个重要障碍。
The relative biological effectiveness (RBE) of protons is highly variable and difficult to quantify. However, RBE is related to the local ionization density, which can be related to the physical measurable dose weighted linear energy transfer (LETD). The aim of this study was to validate the LETD calculations for proton therapy beams implemented in a commercially available treatment planning system (TPS) using microdosimetry measurements and independent LETD calculations (Open-MCsquare (MCS)).The TPS (RayStation v6R) was used to generate treatment plans on the CIRS-731-HN anthropomorphic phantom for three anatomical sites (brain, nasopharynx, neck) for a spherical target (o = 5 cm) with uniform target dose to calculate the LETD distribution. Measurements were performed at the University Medical Center Groningen proton therapy center (Proteus Plus, IBA) using a mu(+)-probe utilizing silicon on insulator microdosimeters capable of detecting lineal energies as low as 0.15 keV mu m(-1) in tissue. Dose averaged mean lineal energy depth-profiles were measured for 70 and 130 MeV spots in water and for the three treatment plans in water and an anthropomorphic phantom. The measurements were compared to the LETD calculated in the TPS and MCS independent dose calculation engine. D center dot was compared to D center dot LETD in terms of a gamma-index with a distance-to-agreement criteria of 2 mm and increasing dose difference criteria to determine the criteria for which a 90% pass rate was accomplished.Measurements of D center dot were in good agreement with the D center dot LETD calculated in the TPS and MCS. The 90% passing rate threshold was reached at different D center dot LETD difference criteria for single spots (TPS: 1% MCS: 1%), treatment plans in water (TPS: 3% MCS: 6%) and treatment plans in an anthropomorphic phantom (TPS: 6% MCS: 1%).We conclude that D center dot LETD calculations accuracy in the RayStation TPS and open MCSquare are within 6%, and sufficient for clinical D center dot LETD evaluation and optimization. These findings remove an important obstacle in the road towards clinical implementation of D center dot LETD evaluation and optimization of proton therapy treatment plans.