Department of Radiation Oncology, Hospital of The University of Pennsylvania, Philadelphia 19104, PA, United States of America.
Phys Med Biol. 2020 Aug 19;65(16):165006. doi: 10.1088/1361-6560/ab9455.
We show the performance and feasibility of a proton arc technique so-called proton monoenergetic arc therapy (PMAT). Monoenergetic partial arcs are selected to place spots at the middle of a target and its potential to enhance the dose-averaged linear energy transfer (LETd) distribution within the target. Single-energy partial arcs in a single 360 degree gantry rotation are selected to deposit Bragg's peaks at the central part of the target to increase LETd values. An in-house inverse planning optimizer seeks for homogeneous doses at the target while keeping the dose to organs at risk (OARs) within constraints. The optimization consists of balancing the weights of spots coming out of selected partial arcs. A simple case of a cylindrical target in a phantom is shown to illustrate the method. Three different brain cancer cases are then considered to produce actual clinical plans, compared to those clinically used with pencil beam scanning (PBS). The relative biological effectiveness (RBE) is calculated according to the microdosimetric kinetic model (MKM). For the ideal case of a cylindrical target placed in a cylindrical phantom, the mean LETd in the target increases from 2.8 keV μm to 4.0 keV μm when comparing a three-field PBS plan with PMAT. This is replicated for clinical plans, increasing the mean RBE-weighted doses to the CTV by 3.1%, 1.7% and 2.5%, respectively, assuming an [Formula: see text] ratio equal to 10 Gy in the CTV. In parallel, LETd to OARs near the distal edge of the tumor decrease for all cases and metrics (mean LETd, L and L). The PMAT technique increases the LETd within the target, being feasible for the production of clinical plans meeting physical dosimetric requirements for both target and OARs. Thus, PMAT increases the RBE within the target, which may lead to a widening of the therapeutic index in proton radiotherapy that would be highlighted for low [Formula: see text] ratios and hyperfractionated schedules.
我们展示了质子弧技术（即质子单能弧治疗 PMAT）的性能和可行性。选择单能部分弧来在靶区的中间放置点，以增强靶区内剂量平均线性能量传递（LETd）分布。在单个 360 度旋转机架旋转中选择单能部分弧以在靶区的中心部分沉积布拉格峰，以增加 LETd 值。内部逆规划优化器在满足危及器官（OAR）剂量限制的情况下，寻求靶区的均匀剂量。优化包括平衡来自选定部分弧的点的权重。然后，为了说明该方法，展示了一个圆柱靶在体模中的简单情况。然后考虑了三个不同的脑癌病例来生成实际的临床计划，并与使用铅笔束扫描（PBS）的临床计划进行比较。根据微剂量动力学模型（MKM）计算相对生物效应（RBE）。对于放置在圆柱体模中的圆柱靶的理想情况，与 PMAT 相比，三野 PBS 计划的靶区内平均 LETd 从 2.8 keV μm 增加到 4.0 keV μm。对于临床计划也进行了复制，假设 CTV 中的 [Formula: see text] 比值等于 10 Gy，CTV 中的平均 RBE 加权剂量分别增加了 3.1%、1.7%和 2.5%。同时，所有病例和指标（平均 LETd、L 和 L）中肿瘤远端边缘附近 OAR 的 LETd 降低。PMAT 技术增加了靶区内的 LETd，可为满足靶区和 OARs 的物理剂量学要求的临床计划的生产提供可行性。因此，PMAT 增加了靶区内的 RBE，这可能会拓宽质子放射治疗的治疗指数，对于低 [Formula: see text] 比值和超分割方案，这将更加明显。
