一种用于提高被动质子散射治疗肺肿瘤的分次内运动稳定性的射束角度选择方法。

A Beam-Angle-Selection Method to Improve Inter-Fraction Motion Robustness for Lung Tumor Irradiation With Passive Proton Scattering.

机构信息

90618University of Florida Health Proton Therapy Institute, Jacksonville, FL, USA.

Department of Radiation Oncology, University of Florida, Gainesville, FL, USA.

出版信息

Technol Cancer Res Treat. 2020 Jan-Dec;19:1533033820948052. doi: 10.1177/1533033820948052.

DOI:10.1177/1533033820948052

PMID:32844716

原文链接:https://pmc.ncbi.nlm.nih.gov/articles/PMC7453456/

Abstract

In terms of dose distribution, protons are more sensitive to range variations than photons due to their unique properties. The aim of this study was to develop a method to identify patient-specific robust proton beam angles for lung tumor irradiation by investigating the association between water equivalent thickness (WET) variation and inter-fraction motion-induced target dose degradation. Using 3-dimensional computed tomography (3D-CT) images, the impact of WET variations on the target dose coverage of a series of coplanar proton beams was evaluated for 4 patients with lung cancer. Using ray tracing, WET maps, or WET baseline, were estimated for the internal target volume (ITV) at every 5° gantry interval in the axial plane. After calculating the WET baseline, the planning CT was shifted 5 mm in each anterior-posterior (AP), superior-inferior (SI), and left-right (LR) direction, yielding a total of 6 shifted CTs, and differential WET maps between the planning CT and each shifted CT were calculated. Target dose differences were associated with the average WET change between the original planning CT and the shifted CTs for all 360° gantry rotation beams. Target and OAR dose metrics in the ΔWET-guided plans were compared with those of the clinical plans. The WET variation maps showed areas of both high and low WET variations, with overall similar patterns yet individual differences reflecting tumor position differences. For all 4 patients investigated in this study, the coplanar plans demonstrated a strong correlation between WET changes and ITV dose reductions. Target dose coverage was more stable with the ΔWET-guided plan while OAR doses were comparable to the clinical plan. The WET variation maps have been used in this pilot study to identify proton beam angles that are either sensitive or robust to WET changes in proton passive scattering. This work demonstrates the feasibility of using WET variation maps to assist the planner in inter-fraction motion-robust proton beam angle selection.

摘要

在剂量分布方面，由于质子具有独特的特性，因此其对范围变化比光子更为敏感。本研究的目的是通过研究水当量厚度（WET）变化与分次间运动引起的靶区剂量降低之间的关系，开发一种用于识别肺肿瘤照射的患者特异性稳健质子束角度的方法。使用三维计算机断层扫描（3D-CT）图像，针对 4 名肺癌患者，评估了 WET 变化对一系列共面质子束靶区剂量覆盖的影响。使用射线追踪法，在轴向平面的每个 5°机架间隔处估算了内靶区（ITV）的 WET 图或 WET 基线。计算 WET 基线后，在前后（AP）、上下（SI）和左右（LR）方向上将计划 CT 分别移动 5mm，总共产生了 6 个移位 CT，并计算了计划 CT 与每个移位 CT 之间的差分 WET 图。目标剂量差异与原始计划 CT 与所有 360°机架旋转束的移位 CT 之间的平均 WET 变化有关。比较了 ΔWET 引导计划中的靶区和 OAR 剂量指标与临床计划中的剂量指标。WET 变化图显示了高 WET 变化和低 WET 变化的区域，整体相似，但个别差异反映了肿瘤位置的差异。对于本研究中调查的所有 4 名患者，共面计划显示出 WET 变化与 ITV 剂量降低之间存在很强的相关性。在 ΔWET 引导计划中，靶区剂量覆盖更稳定，而 OAR 剂量与临床计划相当。在这个初步研究中，WET 变化图已用于识别对质子被动散射中的 WET 变化敏感或稳健的质子束角度。这项工作证明了使用 WET 变化图来辅助规划师选择抗分次间运动的质子束角度是可行的。