Doctoral Program in Biomedical Sciences, Graduate School of Comprehensive Human Sciences, University of Tsukuba, Ibaraki, 305-8577, Japan.
Division of Radiation Oncology and Particle Therapy, Exploratory Oncology Research & Clinical Trial Center, National Cancer Center, Chiba, 277-8577, Japan.
Med Phys. 2017 Sep;44(9):4474-4481. doi: 10.1002/mp.12444. Epub 2017 Aug 1.
Hypo-fractionated proton beam therapy (PBT) is an approach that has been increasingly explored over the past decade. It requires high geometric accuracy for targeting of the PBT beams. However, image-guided PBT is currently commonly performed with kV X-ray images of bony anatomy. A dynamic adaptive passive scattering PBT system using computed tomography-based three-dimensional image guidance was developed, and its effectiveness was then evaluated retrospectively in patients with nonsmall cell lung cancer (NSCLC).
The dynamic adaptive PBT system consisted of computed tomography-based image registration and proton dose calculation using a simplified Monte Carlo algorithm, with a range adaptation system that could adjust the range shifter thickness to alter the dose distribution. Three patients were retrospectively analyzed. All plans, which each had a total dose of 60 Gy (relative biological effectiveness; RBE), were generated using two fields (Gantry angles: 270 degree and 180 degree) in a passive scattering method. Three dose distributions were generated for each patient according to the following different registrations: bone registration, tumor registration, and tumor registration with range adaptation. The following dosimetric parameters were compared with the original plan: target dose coverage at D95% for the clinical target volume (CTV), homogeneity of D5% to D95% for the CTV, and dose distributions in normal tissue (Dmax of Spinal cord and V20 Gy of lung).
For the bone registration method, the average D95% and D5% to D95% for the CTV showed average differences from the original plan of -3.7 ± 4.1 Gy (mean ± 1SD; RBE) and 3.6 ± 3.9 Gy (RBE) respectively. The tumor registration method achieved better coverage than the bone registration method, although the dosimetric parameters for coverage and homogeneity still showed average differences in -2.0 ± 2.3 Gy (RBE) and 1.9 ± 2.2 Gy (RBE) respectively. The range adaptive plan showed comparable coverage and homogeneity [D95%: -1.0 ± 1.3 Gy (RBE) and D5% to D95%: 0.9 ± 1.0 Gy (RBE) on average] to the original plan, as well as demonstrating similar normal tissue sparing. The approach could be completed in less than 10 min, including CT acquisition, image registration, dose recalculation with range optimization, and the operator's visual verification.
The tumor dose coverage in patients with NSCLC may deteriorate as a result of respiratory or body movement if daily proton range adaptation is not performed. Our approach may provide higher geometric accuracy for localization of the tumor, and the dynamic range adaptation enables us to achieve the planned dose distribution for hypo-fractionated PBT in the lung.
调强质子束治疗（PBT）是过去十年中越来越受到关注的一种方法。它需要高精度的几何定位来靶向 PBT 射束。然而，目前的图像引导 PBT 通常使用骨性解剖结构的千伏 X 射线图像进行。本研究开发了一种基于 CT 的三维图像引导的动态自适应被动散射 PBT 系统，并对 3 例非小细胞肺癌（NSCLC）患者进行了回顾性评估。
该动态自适应 PBT 系统包括基于 CT 的图像配准和使用简化蒙特卡罗算法进行质子剂量计算，以及可调节射程移位器厚度以改变剂量分布的射程自适应系统。对 3 例患者进行了回顾性分析。所有计划（相对生物效应；RBE）的总剂量为 60 Gy，均采用 2 个射野（机架角度：270 度和 180 度）在被动散射方法下生成。根据以下不同的注册方式为每位患者生成了 3 种剂量分布：骨注册、肿瘤注册和带有射程自适应的肿瘤注册。将以下剂量学参数与原始计划进行了比较：临床靶区（CTV）的 D95%靶区剂量覆盖率、CTV 的 D5%至 D95%的均匀性以及正常组织的剂量分布（脊髓的 Dmax 和肺的 V20 Gy）。
对于骨注册方法，CTV 的平均 D95%和 D5%至 D95%与原始计划相比，平均分别有-3.7 ± 4.1 Gy（均数±1SD；RBE）和 3.6 ± 3.9 Gy（RBE）的差异。肿瘤注册方法的覆盖范围优于骨注册方法，尽管覆盖范围和均匀性的剂量学参数仍然分别有-2.0 ± 2.3 Gy（RBE）和 1.9 ± 2.2 Gy（RBE）的平均差异。范围自适应计划的覆盖范围和均匀性与原始计划相当[D95%：-1.0 ± 1.3 Gy（RBE）和 D5%至 D95%：0.9 ± 1.0 Gy（RBE）]，并且正常组织的保护作用相似。该方法可以在不到 10 分钟的时间内完成，包括 CT 采集、图像配准、带范围优化的剂量重新计算以及操作人员的视觉验证。
如果不进行每日质子射程自适应，非小细胞肺癌患者的肿瘤剂量覆盖可能会因呼吸或身体运动而恶化。我们的方法可能为肿瘤的定位提供更高的几何精度，并且动态范围自适应使我们能够实现肺部的调强 PBT 计划剂量分布。
