在并行 linac-MR 治疗期间,组织接口的剂量干扰:"横向散射电子回归效应" (LS-ERE)
Stephen Steciw1,2, B Gino Fallone1,2, Eugene Yip1,2
1Medical Physics Division, Department of Oncology, University of Alberta, Edmonton, Alberta, Canada.
Medical physics
|August 17, 2024
概括
在并行 linac-MR (LMR-B) 系统中发现了一种新的不对称剂量干扰,即侧向散射电子回归效应 (LS-ERE). 对LS-ERE的认识对于放射治疗中准确的治疗计划至关重要.
科学领域:
- 医学物理 医学物理
- 辐射瘤学 辐射瘤学
- 医疗成像医学成像
背景情况:
- 医疗线性加速器 (linacs) 与用于放射治疗的磁共振成像 (MR) 集成,创建平行 (LMR-B) 和垂直 (LMR-B) 系统.
- 在LMR-B系统中,MR的磁场可以由于电子回归效应 (ERE) 和电子流效应 (ESE) 等效应而扰乱辐射剂量传递.
- 在LMR-B系统中观察到剂量结合效应,但在材料接口的特定不对称剂量扰动没有得到很好的描述.
研究的目的:
- 报告一种新的不对称剂量扰动,称为侧向散射电子回归效应 (LS-ERE),发生在并行linac-MR (LMR-B) 系统中的材料接口.
- 量化LS-ERE及其对磁场强度,磁场大小和材料接口的依赖.
- 研究LS-ERE取消的方法,并将其与其他磁场诱导的剂量干扰进行比较.
主要方法:
- 使用BEAMnrc和EGSnrc蒙特卡罗 (MC) 代码来模拟0.5T和1.5T的0.5-T linac-MR中的6FFF光束.
- 模拟了各种幻影材料-接口组合和场尺寸,包括调制场,以在患者特定的CT数据集 (头部,乳房,肺部) 中量化LS-ERE.
- 用GafChromic薄膜测量在0.5T LMR-B系统中的水-空气接口上的验证的MC模拟和对LMR-B系统的模拟ERE进行比较.
主要成果:
- 发现LS-ERE在很大程度上与场面大小无关,场面大于1x1cm2,在0.5T/1.5T的组织-空气接口的不对称性高达±9.0%,在0.5T/1.5T的组织-肺接口的不对称性为±4.1%.
- 随着磁场强度的增加,LS-ERE的大小和范围下降,随着密度梯度的增加而增加.
- 像对立 (POP) 场和磁场逆转等技术有效地减少了LS-ERE不对称性. 在观察到的皮肤剂量增加中,LS-ERE的贡献约为30%.
结论:
- 侧向散射电子回归效应 (LS-ERE) 是平行 linac-MR (LMR-B) 系统中材料接口存在的显著剂量扰动.
- 了解和考虑LS-ERE对于准确的治疗计划系统 (TPS) 在LMR-B治疗中的评估至关重要,特别是在组织密度梯度的区域.
- 这些发现强调了考虑这些特定剂量干扰对于安全有效的MR导向放射治疗的重要性.
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