Medical Physics Laboratory, Medical School, National and Kapodistrian University of Athens, Athens, Greece.
Department of Radiotherapy, Alexandra Hospital, Athens, Greece.
PLoS One. 2024 Nov 7;19(11):e0313260. doi: 10.1371/journal.pone.0313260. eCollection 2024.
Due to its inherent technical challenges, craniospinal irradiation (CSI) entails crucial considerations regarding plan complexity and robustness. The scope of this work was to establish and validate methods suitable for the evaluation of robustness, as well as for dose verification in CSI with VMAT. Five patients previously treated with CSI were retrospectively selected. For each patient, two technically different treatment plans were generated, based on the conventional (static overlap) and staggered (dynamic overlap) configuration. These techniques served as a benchmark to evaluate the potential of a metric proposed in this work, aimed at quantifying robustness, the Overlap Robustness Index (ORI). Furthermore, they were utilized to assess the suitability of two experimental methods relying on film dosimetry, as well as on Delta4 phantom for identifying sources of uncertainties in CSI applications. In accordance with the positional error simulation performed, the staggered approach yielded a statistically significant superior ORI value compared to the conventional one. Additionally, the strong correlation observed between the positional shift induced dose distribution changes and ORI results (Spearman's r = -0.941, p-value < 0.001) demonstrated the sensitivity of ORI in detecting areas of steep dose gradients within the overlapping regions that could potentially compromise the quality of treatment. Concerning dose verification, analysis in terms of dose profiles revealed a superior dosimetric accuracy for the staggered technique relative to conventional for both film and Delta4 measurements. Film-based gamma index results showed that staggered technique outperformed the conventional for the majority of passing criteria considered, with differences in passing rates up to 8.1%. The two treatment techniques however, exhibited equivalent dose delivery accuracy for the clinically relevant passing criteria when Delta4 was employed, with passing rate differences less than 0.6%. Findings of this study revealed that ORI is suitable for quantifying robustness in CSI with VMAT, while radiochromic films appeared to be the best candidate for CSI dose verification in this work.
由于其固有的技术挑战，颅脊髓照射（CSI）需要考虑计划复杂性和稳健性等关键因素。本工作的目的是建立和验证适合评估稳健性以及用于 CSI 容积旋转调强放疗（VMAT）剂量验证的方法。回顾性选择了 5 例先前接受 CSI 治疗的患者。对于每位患者，根据常规（静态重叠）和交错（动态重叠）配置生成了两种技术上不同的治疗计划。这些技术用作基准，用于评估本文提出的旨在量化稳健性的度量标准——重叠稳健性指数（ORI）的潜力。此外，还利用它们评估了两种基于胶片剂量学和 Delta4 体模的实验方法的适用性，以确定 CSI 应用中不确定性的来源。根据进行的位置误差模拟，交错方法的 ORI 值明显优于常规方法。此外，观察到诱导的位置偏移剂量分布变化与 ORI 结果之间的强相关性（Spearman r = -0.941，p 值 < 0.001）表明 ORI 能够灵敏地检测到重叠区域内潜在危及治疗质量的陡峭剂量梯度区域。关于剂量验证，剂量分布曲线的分析表明，交错技术在胶片和 Delta4 测量方面相对于常规技术具有更高的剂量学准确性。胶片伽玛指数结果表明，对于大多数考虑的通过标准，交错技术的通过率优于常规技术，通过率差异高达 8.1%。然而，当使用 Delta4 时，两种治疗技术对于临床相关的通过标准具有相同的剂量输送准确性，通过率差异小于 0.6%。本研究的结果表明，ORI 适合于量化 CSI 中 VMAT 的稳健性，而放射色氨酸胶片似乎是本工作中 CSI 剂量验证的最佳候选方法。
