Medical Radiation Physics, Department of Physics, Stockholm University, Stockholm, Sweden.
Medical Radiation Physics, Department of Physics, Stockholm University, Stockholm, Sweden; RaySearch Laboratories AB, Stockholm, Sweden.
Phys Med. 2018 Dec;56:81-89. doi: 10.1016/j.ejmp.2018.10.025. Epub 2018 Nov 22.
Interlaced beams have previously been proposed for delivering proton grid therapy. This study aims to assess dose-averaged LET (LET) and RBE-weighted dose (D) distributions of such beam geometries, and compare them with conventional intensity modulated proton therapy (IMPT).
IMPT plans and four different interlaced proton grid therapy plans were generated for five patient cases (esophagus, lung, liver, prostate, anus). The constant RBE = 1.1 was assumed for optimization. The LET was subsequently Monte Carlo calculated for each plan and used as input for two LET-dependent variable RBE models. The fulfilment of clinical goals, along with DVH and spatial distribution evaluations, were then assessed and compared.
All plans fulfilled the clinical target goals assuming RBE = 1.1. The target coverage was slightly compromised for some grid plans when assuming the variable RBE models. All IMPT plans, and 18 of 20 grid plans, fulfilled all clinical goals for the organs at risk when assuming RBE = 1.1, whereas most plans failed at least one goal when assuming the variable RBE models. Compared with the IMPT plans, the grid plans demonstrated substantially different LET distributions due to the fundamentally different beam geometries. However, D distributions in the target were similar.
Despite the unconventional beam geometries of interlaced proton grid plans, with resulting alternating dose and LET patterns, the fulfillment of realistic clinical goals seems to be comparable to regular IMPT plans, both assuming RBE = 1.1 and variable RBE models. In addition, the alternating grid patterns do not seem to give rise to unexpected D hot-spots.
交错射束先前已被提议用于递送质子栅格治疗。本研究旨在评估此类射束几何形状的剂量平均线性能量传递（LET）和重加权剂量（D）分布，并将其与常规强度调制质子治疗（IMPT）进行比较。
为五个患者病例（食管、肺、肝、前列腺、肛门）生成了 IMPT 计划和四个不同的交错质子栅格治疗计划。假设恒定 RBE=1.1 进行优化。随后，对每个计划进行了蒙特卡罗计算以获得 LET，并将其用作两个依赖 LET 的可变 RBE 模型的输入。然后评估和比较了满足临床目标以及剂量体积直方图（DVH）和空间分布评估的情况。
当假设 RBE=1.1 时，所有计划都满足了临床靶区目标。当假设可变 RBE 模型时，对于一些栅格计划，靶区覆盖略有受损。当假设 RBE=1.1 时，所有 IMPT 计划和 20 个栅格计划中的 18 个都满足了危及器官的所有临床目标，而当假设可变 RBE 模型时，大多数计划至少有一个目标失败。与 IMPT 计划相比，由于基本不同的射束几何形状，栅格计划显示出截然不同的 LET 分布。然而，靶区内的 D 分布相似。
尽管交错质子栅格计划具有非常规的射束几何形状，导致剂量和 LET 交替模式，但在假设 RBE=1.1 和可变 RBE 模型的情况下，实现现实临床目标似乎与常规 IMPT 计划相当。此外，交替栅格模式似乎不会导致意外的 D 热点。
