Radiotherapy and Radiosurgery Department, Humanitas Clinical and Research Center, IRCSS, Milan-Rozzano, Italy.
Department of Biomedical Sciences, Humanitas University, Milan-Rozzano, Italy.
Technol Cancer Res Treat. 2020 Jan-Dec;19:1533033820980412. doi: 10.1177/1533033820980412.
To investigate the role of intensity-modulated proton therapy (IMPT) for hepatocellular carcinoma (HCC) patients to be treated with stereotactic body radiation therapy (SBRT) in a risk-adapted dose prescription regimen.
A cohort of 30 patients was retrospectively selected as "at-risk" of dose de-escalation due to the proximity of the target volumes to dose-limiting healthy structures. IMPT plans were compared to volumetric modulated arc therapy (VMAT) RapidArc (RA) plans. The maximum dose prescription foreseen was 75 Gy in 3 fractions. The dosimetric analysis was performed on several quantitative metrics on the target volumes and organs at risk to identify the relative improvement of IMPT over VMAT and to determine if IMPT could mitigate the need of dose reduction and quantify the consequent potential patient accrual rate for protons.
IMPT and VMAT plans resulted in equivalent target dose distributions: both could ensure the required coverage for CTV and PTV. Systematic and significant improvements were observed with IMPT for all organs at risk and metrics. An average gain of 9.0 ± 11.6, 8.5 ± 7.7, 5.9 ± 7.1, 4.2 ± 6.4, 8.9 ± 7.1, 6.7 ± 7.5 Gy was found in the near-to-maximum doses for the ribs, chest wall, heart, duodenum, stomach and bowel bag respectively. Twenty patients violated one or more binding constraints with RA, while only 2 with IMPT. For all these patients, some dose de-intensification would have been required to respect the constraints. For photons, the maximum allowed dose ranged from 15.0 to 20.63 Gy per fraction while for the 2 proton cases it would have been 18.75 or 20.63 Gy.
The results of this in-silico planning study suggests that IMPT might result in advantages compared to photon-based VMAT for HCC patients to be treated with ablative SBRT. In particular, the dosimetric characteristics of protons may avoid the need for dose de-escalation in a risk-adapted prescription regimen for those patients with lesions located in proximity of dose-limiting healthy structures. Depending on the selection thresholds, the number of patients eligible for treatment at the full dose can be significantly increased with protons.
探讨在适应风险的剂量处方方案中，调强质子治疗（IMPT）在立体定向体部放射治疗（SBRT）治疗肝细胞癌（HCC）患者中的作用。
回顾性选择了 30 例患者作为“高危”患者，由于靶区与剂量限制的健康结构接近，因此需要降低剂量。比较了调强质子治疗（IMPT）计划与容积调强弧形治疗（VMAT）RapidArc（RA）计划。预计最大剂量处方为 75 Gy，分 3 次。对靶区和危及器官进行了几种定量指标的剂量分析，以确定 IMPT 相对于 VMAT 的相对改善，并确定 IMPT 是否可以减轻剂量降低的需求，并量化质子治疗的潜在患者入组率。
IMPT 和 VMAT 计划导致了等效的靶区剂量分布：两者都可以确保 CTV 和 PTV 的所需覆盖。对于所有危及器官和指标，IMPT 均观察到系统且显著的改善。肋骨、胸壁、心脏、十二指肠、胃和肠袋的近最大剂量分别平均增加 9.0 ± 11.6、8.5 ± 7.7、5.9 ± 7.1、4.2 ± 6.4、8.9 ± 7.1、6.7 ± 7.5 Gy。20 例患者的 RA 违反了一个或多个约束条件，而只有 2 例患者的 IMPT 违反了一个或多个约束条件。对于所有这些患者，都需要降低剂量以遵守约束条件。对于光子，每个分次的最大允许剂量范围为 15.0 至 20.63 Gy，而对于 2 个质子病例，最大允许剂量将为 18.75 或 20.63 Gy。
这项计算机模拟计划研究的结果表明，与基于光子的 VMAT 相比，IMPT 可能为接受消融性 SBRT 治疗的 HCC 患者带来优势。特别是，质子的剂量学特性可以避免在适应风险的处方方案中对位于剂量限制的健康结构附近的病变患者进行剂量降低。根据选择阈值，使用质子治疗可以显著增加符合全剂量治疗条件的患者数量。
