Monte Carlo modeling of a 6 and 18 MV Varian Clinac medical accelerator for in-field and out-of-field dose calculations: development and validation.
Monte Carlo modeling of a 6 and 18 MV Varian Clinac medical accelerator for in-field and out-of-field dose calculations: development and validation.
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DOI：
10.1088/0031-9155/54/4/n01
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发表时间：
2009-02-21
影响因子：
3.5
通讯作者：
Xu XG
中科院分区：
文献类型：
--
作者：
Bednarz B;Xu XG
人们越来越担心放射诱发的第二次癌症和与放射治疗相关的晚期组织损伤的风险增加。为了更好地理解和更准确地量化由医疗加速器的散射和泄漏辐射引起的非目标器官剂量，需要医疗直线加速器的详细蒙特卡罗模型。本文介绍了在 6 和 18 MV 光束能量下运行的 Varian Clinac 详细加速器模型的开发和验证。使用蒙特卡罗代码 MCNPX 定义和集成了 100 多个加速器组件。进行了一系列现场和场外剂量验证研究。使用加速器模型计算的现场剂量分布经过调整，以匹配测量数据，这些数据被认为是制造商提供的 Varian Clinac 加速器事实上的“黄金标准”。考虑的场地尺寸为 4 cm × 4 cm、10 cm × 10 cm、20 cm × 20 cm 和 40 cm × 40 cm。所有位置的百分比深度剂量曲线上的计算剂量和测量剂量之间的局部差异均小于 2%。所有位置的剂量分布曲线上计算剂量与测量剂量之间的局部差异在平台区域小于 2%，在半影区域小于 2 mm。计算了场外剂量分布，并与场尺寸为 4 cm × 4 cm、10 cm × 10 cm 和 20 cm × 20 cm 的两种光束能量的测量数据进行比较。对于本研究中考虑的所有射野大小，6 和 18 MV 光束的计算剂量和测量剂量之间的平均局部差异分别为 14% 和 16%。此外，通过将计算的空气中子注量与报告的计算和测量结果进行比较，验证了确定 18 MV 运行模型中中子污染的方法。计算的中子注量与测量的中子注量之间的平均差异为 20%。作为用于现场和场外剂量计算的最详细的加速器模型之一，该模型将与解剖学上真实的计算患者模型结合到一个计算框架中，以计算各种放射治疗计划中患者的非靶器官剂量。
There is a serious and growing concern about the increased risk of radiation-induced second cancers and late tissue injuries associated with radiation treatment. To better understand and to more accurately quantify non-target organ doses due to scatter and leakage radiation from medical accelerators, a detailed Monte Carlo model of the medical linear accelerator is needed. This paper describes the development and validation of a detailed accelerator model of the Varian Clinac operating at 6 and 18 MV beam energies. Over 100 accelerator components have been defined and integrated using the Monte Carlo code MCNPX. A series of in-field and out-of-field dose validation studies were performed. In-field dose distributions calculated using the accelerator models were tuned to match measurement data that are considered the de facto ‘gold standard’ for the Varian Clinac accelerator provided by the manufacturer. Field sizes of 4 cm × 4 cm, 10 cm × 10 cm, 20 cm × 20 cm and 40 cm × 40 cm were considered. The local difference between calculated and measured dose on the percent depth dose curve was less than 2% for all locations. The local difference between calculated and measured dose on the dose profile curve was less than 2% in the plateau region and less than 2 mm in the penumbra region for all locations. Out-of-field dose profiles were calculated and compared to measurement data for both beam energies for field sizes of 4 cm × 4 cm, 10 cm × 10 cm and 20 cm × 20 cm. For all field sizes considered in this study, the average local difference between calculated and measured dose for the 6 and 18 MV beams was 14 and 16%, respectively. In addition, a method for determining neutron contamination in the 18 MV operating model was validated by comparing calculated in-air neutron fluence with reported calculations and measurements. The average difference between calculated and measured neutron fluence was 20%. As one of the most detailed accelerator models for both in-field and out-of-field dose calculations, the model will be combined with anatomically realistic computational patient phantoms into a computational framework to calculate non-target organ doses to patients from various radiation treatment plans.