Department of Radiation Oncology, University of Florida College of Medicine, Jacksonville, FL, USA.
School of Physical Sciences, University of Science and Technology of China, Hefei, China.
Acta Oncol. 2021 Feb;60(2):252-259. doi: 10.1080/0284186X.2020.1834141. Epub 2020 Oct 16.
To evaluate the LETd-weighted biological dose to OARs in proton therapy for breast cancer and to study the relationship of the LETd-weighted biological dose relative to the standard dose (RBE = 1.1) and thereby to provide estimations of the biological dose uncertainties with the standard dose calculations (RBE = 1.1) commonly used in clinical practice.
This study included 20 patients who received IMPT treatment to the whole breast/chest wall and regional lymph nodes. The LETd distributions were calculated along with the physical dose using an open-source Monte Carlo simulation package, MCsquare. Using the McMahon linear model, the LETd-weighted biological dose was computed from the physical dose and LETd. OAR doses were compared between the Dose (RBE = 1.1) and the LETd-weighted biological dose, on brachial plexus, rib, heart, esophagus, and Ipsilateral lung.
On average, the LETd-weighted biological dose compared to the Dose (RBE = 1.1) was higher by 8% for the brachial plexus D0.1 cc, 13% for the ribs D0.5 cc, 24% for mean heart dose, and 10% for the esophagus D0.1 cc, respectively. The LETd-weighted doses to the Ipsilateral lung V5, V10, and V20 were comparable to the Dose (RBE = 1.1). No statistically significant difference in biological dose enhancement to OARs was observed between the intact breast group and the CW group, with the exception of the ribs: the CW group experienced slightly greater biological dose enhancement (13% vs. 12%, = 0.04) to the ribs than the intact breast group.
Enhanced biological dose was observed compared to standard dose with assumed RBE of 1.1 for the heart, ribs, esophagus, and brachial plexus in breast/CW and regional nodal IMPT plans. Variable RBE models should be considered in the evaluation of the IMPT breast plans, especially for OARs located near the end of range of a proton beam. Clinical outcome studies are needed to validate model predictions for clinical toxicities.
评估乳腺癌质子治疗中 OAR 的 LETd 加权生物剂量，并研究 LETd 加权生物剂量与标准剂量（RBE=1.1）的关系，从而提供对临床实践中常用的标准剂量计算（RBE=1.1）的生物剂量不确定性的估计。
本研究纳入了 20 名接受全乳/胸壁和区域淋巴结调强质子治疗的患者。使用开源蒙特卡罗模拟软件包 MCsquare 计算了物理剂量和 LETd 分布。利用 McMahon 线性模型，从物理剂量和 LETd 计算出 LETd 加权生物剂量。比较了臂丛神经、肋骨、心脏、食管和同侧肺在剂量（RBE=1.1）和 LETd 加权生物剂量之间的剂量。
平均而言，臂丛神经 D0.1cc 的 LETd 加权生物剂量比剂量（RBE=1.1）高 8%，肋骨 D0.5cc 的 LETd 加权生物剂量高 13%，平均心脏剂量高 24%，食管 D0.1cc 的 LETd 加权生物剂量高 10%。同侧肺 V5、V10 和 V20 的 LETd 加权剂量与剂量（RBE=1.1）相当。除了肋骨，在完整乳房组和胸壁/锁骨区组之间没有观察到 OAR 生物剂量增强的统计学差异：胸壁/锁骨区组的肋骨生物剂量增强略高（13%比 12%，=0.04）。
与假设 RBE 为 1.1 的标准剂量相比，在乳腺癌/CW 和区域淋巴结调强质子治疗计划中，心脏、肋骨、食管和臂丛神经的生物剂量增强。在评估 IMPT 乳房计划时，应考虑可变 RBE 模型，特别是对于质子束末端附近的 OAR。需要临床结局研究来验证模型预测对临床毒性的影响。
