Xiao Feng, Chang Yu, Zhang Sheng, Yang Zhiyong
Medical Physics, School of Physics and Technology, Wuhan University, Wuhan, 430072, China.
Cancer Center, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430022, China.
J Appl Clin Med Phys. 2021 Jan;22(1):210-217. doi: 10.1002/acm2.13136. Epub 2021 Jan 11.
We conducted this study to construct a target coverage-volume histogram (CVH) and leakage-volume histogram (LVH) metrics and optimization strategy for the selection of the Iris collimator in Cyberknife Xsight lung tracking treatment through a retrospective analysis of target structures and clinical data.
CVH and LVH metrics were retrospectively analyzed for 37 lung cancer patients. CVH and LVH were the same as dose-volume histogram (DVH), but with a coverage and leakage replacing dose. For each patient, Iris collimator was optimized and selected based on CVH and LVH metrics. The CVH and LVH metrics were then compared to ascertain differences in 95% (C95) or 90% (C90) of the target coverage thresholds. The planning target volume (PTV) C95 and C90 coverage, absolute mean leakage value, leakage/coverage ratio, selected collimator diameter (Φ), Φ/length of the long axis of PTV (A ), and Φ/length of the short axis (A ) of PTV were compared. The correlation of the absolute mean leakage value, leakage/coverage ratio, Φ/A and Φ/A were evaluated.
For each patient, the PTV C95 coverage (70.45 vs 63.19) and C90 coverage (77.25 vs 69.96) were higher in the C95 coverage threshold group compared to the C90 coverage threshold group. The leakage/coverage ratio (0.56 vs 0.69) and absolute mean leakage value (0.56 vs 0.61) were lower in C90 coverage threshold group than in C95 coverage threshold group. The Spearmen correlation test showed the Φ/A were significantly correlated with leakage/coverage ratio and absolute mean leakage value. Upon analysis of the selected collimator diameters, the mean value of Φ/A of the optimized collimator diameters was found to be 1.10.
The CVH and LVH analysis is able to quantitatively evaluate the tradeoff between target coverage and normal tissue sparing.
通过对靶区结构和临床数据的回顾性分析，构建用于在射波刀Xsight肺部追踪治疗中选择虹膜准直器的靶区覆盖体积直方图（CVH）和漏射体积直方图（LVH）指标及优化策略。
对37例肺癌患者的CVH和LVH指标进行回顾性分析。CVH和LVH与剂量体积直方图（DVH）类似，但用覆盖和漏射取代剂量。对于每位患者，基于CVH和LVH指标对虹膜准直器进行优化和选择。然后比较CVH和LVH指标，以确定在95%（C95）或90%（C90）靶区覆盖阈值方面的差异。比较计划靶区（PTV）的C95和C90覆盖率、绝对平均漏射值、漏射/覆盖比、所选准直器直径（Φ）、Φ/PTV长轴长度（A ）以及Φ/PTV短轴长度（A ）。评估绝对平均漏射值、漏射/覆盖比、Φ/A 和Φ/A 之间的相关性。
对于每位患者，C95覆盖阈值组的PTV C95覆盖率（70.45对63.19）和C90覆盖率（77.25对69.96）高于C90覆盖阈值组。C90覆盖阈值组的漏射/覆盖比（0.56对0.69）和绝对平均漏射值（0.56对0.61）低于C95覆盖阈值组。Spearmen相关性检验表明，Φ/A 与漏射/覆盖比和绝对平均漏射值显著相关。在分析所选准直器直径时，发现优化后的准直器直径的Φ/A 平均值为1.10。
CVH和LVH分析能够定量评估靶区覆盖与正常组织保护之间的权衡。
