Technical Note: Dose effects of 1.5 T transverse magnetic field on tissue interfaces in MRI-guided radiotherapy
Technical Note: Dose effects of 1.5 T transverse magnetic field on tissue interfaces in MRI-guided radiotherapy
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DOI：
10.1118/1.4959534
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发表时间：
2016-08-01
期刊：
影响因子：
3.8
通讯作者：
Li, X. Allen
中科院分区：
文献类型：
--
作者：
Chen, Xinfeng;Prior, Phil;Li, X. Allen
目的：MRI与直线加速器（MR-直线加速器）的集成为高精度放射治疗（RT）提供了巨大的潜力。然而，由于横向磁场（ERF）的存在而导致的电子偏转会影响剂量分布，特别是组织界面处的电子返回效应（ERE）。本研究的目的是调查的剂量效应的ERE在空气组织和肺组织接口在调强放射治疗（IMRT）planning.Methods：IMRT和体积调制弧治疗（VMAT）计划为代表的胰腺，肺，乳腺，头颈部（HN）的情况下，产生以下常用的临床剂量体积（DV）标准。在每种情况下，生成了三种类型的计划：（1）在没有重新计算的情况下生成的原始计划;（2）通过重新计算原始计划生成的重建计划，其中存在1.5 T的重新计算（无优化）;以及（3）通过完全优化生成的优化计划，其中重新计算= 1.5 T。使用各种DV参数比较这些计划，包括OAR（风险器官）和组织界面中的V-100%、D-95%、DHI [剂量异质性指数：（D-20%-D-80%）/D-处方]、D-max和D-1cc。本工作中的所有优化和计算都是在静态数据上进行的。结果：TMF下的剂量重新计算显示，1.5 T TMF的存在可以略微降低PTV的V-100%和D-95%，除一例肺病例外，所有病例的差异均小于4%。在所有情况下，TMF都会导致皮肤上的D-max和D-1cc显着增加，大多在10%到35%之间。空气腔壁上的D-max和D-1cc的变化取决于位置、几何形状和尺寸，变化范围高达15%。在胰腺病例中，与固定射束IMRT相比，VMAT计划导致ERE的剂量效应小得多。当在计划优化中考虑放射性物质时，放射性物质在组织界面处的剂量效应（例如，气腔壁，肺组织接口，皮肤）显着减少在大多数cases.Conclusions：组织接口上的剂量可以显着改变MR引导RT过程中的磁场时，不包括在计划优化的存在下，一个闪烁。这些变化可以大大减少，甚至消除在VMAT/IMRT优化，特别是考虑到的干扰，而不会恶化整体计划质量。(C)2016年美国医学物理学家协会。
Purpose: The integration of MRI with a linear accelerator (MR-linac) offers great potential for high-precision delivery of radiation therapy (RT). However, the electron deflection resulting from the presence of a transverse magnetic field (TMF) can affect the dose distribution, particularly the electron return effect (ERE) at tissue interfaces. The purpose of the study is to investigate the dose effects of ERE at air-tissue and lung-tissue interfaces during intensity-modulated radiation therapy (IMRT) planning.Methods: IMRT and volumetric modulated arc therapy (VMAT) plans for representative pancreas, lung, breast, and head and neck (HN) cases were generated following commonly used clinical dose volume (DV) criteria. In each case, three types of plans were generated: (1) the original plan generated without a TMF; (2) the reconstructed plan generated by recalculating the original plan with the presence of a TMF of 1.5 T (no optimization); and (3) the optimized plan generated by a full optimization with TMF = 1.5 T. These plans were compared using a variety of DV parameters, including V-100%, D-95%, DHI [dose heterogeneity index: (D-20%-D-80%)/D-prescription], D-max, and D-1cc in OARs (organs at risk) and tissue interface. All the optimizations and calculations in this work were performed on static data.Results: The dose recalculation under TMF showed the presence of the 1.5 T TMF can slightly reduce V-100% and D-95% for PTV, with the differences being less than 4% for all but one lung case studied. The TMF results in considerable increases in D-max and D-1cc on the skin in all cases, mostly between 10% and 35%. The changes in D-max and D-1cc on air cavity walls are dependent upon site, geometry, and size, with changes ranging up to 15%. The VMAT plans lead to much smaller dose effects from ERE compared to fixed-beam IMRT in pancreas case. When the TMF is considered in the plan optimization, the dose effects of the TMF at tissue interfaces (e.g., air-cavity wall, lung-tissue interfaces, skin) are significantly reduced in most cases.Conclusions: The doses on tissue interfaces can be significantly changed by the presence of a TMF during MR-guided RT when the magnetic field is not included in plan optimization. These changes can be substantially reduced or even eliminated during VMAT/IMRT optimization that specifically considers the TMF, without deteriorating overall plan quality. (C) 2016 American Association of Physicists in Medicine.