Division of Medical Physics in Radiation Oncology, German Cancer Research Center (DKFZ), 69120, Heidelberg, Germany.
Heidelberg Institute for Radiation Oncology (HIRO), National Center for Radiation Research in Oncology (NCRO), 69120, Heidelberg, Germany.
Med Phys. 2017 Dec;44(12):6621-6631. doi: 10.1002/mp.12631. Epub 2017 Nov 20.
Magnetic resonance image-guided radiotherapy (MRgRT) has the potential to increase the accuracy of radiation treatment delivery. Several research groups have developed hybrid MRgRT devices differing by radiation source used and magnetic field orientation and strength. In this work, we investigate the impact of different magnetic field orientations and strengths on the treatment planning of nonsmall cell lung cancer patients (NSCLC).
A framework using the in-house developed treatment planning system matRad and the EGSnrc Monte Carlo code system was introduced to perform Monte Carlo-based treatment planning in the presence of a magnetic field. A specialized spectrum-based source model for the beam qualities of 6 MV and cobalt-60 was applied. Optimized plans for stereotactic body radiation therapy (SBRT) and intensity-modulated radiation therapy (IMRT) were generated for four NSCLC patients in the presence of different magnetic field orientations and strengths which are applied in hybrid MRgRT devices currently under development or in clinical use.
SBRT and IMRT treatment planning could be performed with consistent plan quality for all magnetic field setups. Only minor effects on the treatment planning outcome were found in the case of magnetic fields orientated perpendicular to the beam direction. Compared to the perpendicular magnetic field orientation, the inline orientation showed the capability to reduce the dose to lung while maintaining equal target coverage. Particularly for tumors with a central position in lung, a distinct dose reduction was obtained which led to a maximum reduction of mean lung dose by 18.5% (0.5 Gy), when applying a 1 T inline magnetic field.
All plans generated in this work obtained dose metrics within clinical constraints according to RTOG guidelines. When considering conventional dose metrics, no detrimental effects due to the magnetic fields were observed on the dose to the tumor or to organs at risk. An evaluation of the effects on skin dose was not ascertainable due to the simplified specification of the source model used. By accounting for the magnetic field during treatment planning, a dose reduction in lung could be achieved for inline-oriented magnetic fields. An inline orientation of the magnetic field therefore showed a potential benefit when treating NSCLC with MRgRT.
磁共振引导放射治疗（MRgRT）有可能提高放射治疗的准确性。几个研究小组已经开发出了不同的混合 MRgRT 设备，其区别在于所使用的辐射源以及磁场的方向和强度。在这项工作中，我们研究了不同磁场方向和强度对非小细胞肺癌（NSCLC）患者治疗计划的影响。
我们引入了一个使用内部开发的治疗计划系统 matRad 和 EGSnrc 蒙特卡罗代码系统的框架，以便在存在磁场的情况下进行基于蒙特卡罗的治疗计划。应用了一种专门的基于谱的源模型，用于模拟 6 MV 和钴-60 的束质。针对目前正在开发或临床使用的混合 MRgRT 设备中存在的不同磁场方向和强度，为四名 NSCLC 患者生成了立体定向体部放射治疗（SBRT）和调强放射治疗（IMRT）的优化计划。
对于所有磁场设置，都可以进行 SBRT 和 IMRT 治疗计划，并且计划质量一致。只有在磁场方向垂直于射束方向的情况下，治疗计划结果才会出现较小的影响。与垂直磁场方向相比，在线性磁场方向下，能够降低肺部剂量，同时保持靶区覆盖相同。特别是对于位于肺部中央的肿瘤，当施加 1 T 在线性磁场时，可以获得明显的剂量降低，导致平均肺剂量最大降低 18.5%（0.5 Gy）。
根据 RTOG 指南，本工作中生成的所有计划都获得了在临床限制内的剂量指标。在考虑常规剂量指标时，没有观察到磁场对肿瘤或危及器官的剂量产生不利影响。由于所使用的源模型的简化规格，无法确定对皮肤剂量的影响评估。通过在治疗计划中考虑磁场，可以在线性磁场方向上实现肺部剂量的降低。因此，当使用 MRgRT 治疗 NSCLC 时，磁场的线性方向显示出潜在的益处。
