German Cancer Research Center (DKFZ), Heidelberg, Germany.
National Center for Radiation Research in Oncology (NCRO), Heidelberg Institute for Radiation Oncology (HIRO), Heidelberg, Germany.
Med Phys. 2022 Mar;49(3):1853-1873. doi: 10.1002/mp.15398. Epub 2022 Jan 21.
To present a first study on the treatment planning feasibility in perpendicular field MRI-integrated proton therapy that considers the full transport of protons from the pencil beam scanning (PBS) assembly to the patient inside the MRI scanner.
A generic proton PBS gantry was modeled as being integrated with a realistic split-bore MRI system in the perpendicular orientation. MRI field strengths were modeled as 0.5, 1, and 1.5 T. The PBS beam delivery and dose calculation was modeled using the TOPAS Monte Carlo toolkit coupled with matRad as the optimizer engine. A water phantom, liver, and prostate plans were evaluated and optimized in the presence of the full MRI field distribution. A simple combination of gantry angle offset and small PBS nozzle skew was used to direct the proton beams along a path that closely follows the reference planning scenario, that is, without magnetic field.
All planning metrics could be successfully achieved with the inclusion of gantry angle offsets in the range of 8 -29 when coupled with a PBS nozzle skew of 1.6 -4.4 . These two hardware-based corrections were selected to minimize the average Euclidean distance (AED) in the beam path enabling the proton beams to travel inside the patient in a path that is close to the original path (AED smaller than 3 mm at 1.5 T). Final dose optimization, performed through further changes in the PBS delivery, was then shown to be feasible for our selection of plans studied yielding comparable plan quality metrics to reference conditions.
For the first time, we have shown a robust method to account for the full proton beam deflection in a perpendicular orientation MRI-integrated proton therapy. These results support the ongoing development of the current prototype systems.
介绍首次在垂直场 MRI 集成质子治疗中进行治疗计划可行性的研究，该研究考虑了从铅笔束扫描（PBS）组件到 MRI 扫描仪内部患者的质子完全传输。
将通用质子 PBS 龙门架建模为与垂直方向的现实分体孔 MRI 系统集成。MRI 场强建模为 0.5、1 和 1.5 T。使用 TOPAS 蒙特卡罗工具包与 matRad 作为优化引擎对 PBS 束传输和剂量计算进行建模。在存在全 MRI 场分布的情况下，对水模体、肝脏和前列腺计划进行评估和优化。使用龙门架角度偏移和小 PBS 喷嘴偏斜的简单组合，将质子束引导至沿参考规划方案（即无磁场）的路径。
当与 PBS 喷嘴偏斜为 1.6 -4.4 结合使用时，通过在 8 -29 的范围内使用龙门架角度偏移，可以成功实现所有计划指标。这两个基于硬件的校正被选择为最小化光束路径中的平均欧几里得距离（AED），从而使质子束能够在接近原始路径的患者内部沿路径传输（在 1.5 T 时 AED 小于 3 毫米）。然后，通过进一步改变 PBS 传输，对最终剂量优化进行了研究，结果表明，对于我们研究的计划选择，这是可行的，并且可以得到与参考条件相当的计划质量指标。
我们首次展示了一种在垂直场 MRI 集成质子治疗中可靠地考虑质子束完全偏转的方法。这些结果支持当前原型系统的持续开发。
