CNAO, National Center for Oncological Hadrontherapy, Pavia, Italy.
CNAO, National Center for Oncological Hadrontherapy, Pavia, Italy.
Radiother Oncol. 2020 May;146:213-220. doi: 10.1016/j.radonc.2020.02.025. Epub 2020 Mar 26.
To investigate the impact of four-dimensional robust optimization (4DRO) on dose delivered to lung cancer patients in pencil beam scanning proton therapy.
2 strategies were compared for 20 lung cancer patients, using a different number of breathing phases of the reconstructed 4D computed tomography (CT) included in the plan optimization problem. In the restricted approach combined with gating, only 3 phases close to reference end-exhale were considered instead of the whole breathing cycle. The prescribed dose was 60 Gy(RBE) in 10 fractions. Target coverage (D98%) and dose to healthy tissues were evaluated using Wilcoxon signed-rank test. To assess the robustness against interfractional anatomical and respiratory variations, the optimized plans were recalculated on re-evaluation 4DCTs. To compare the sensitivity of both strategies to interplay effects, we implemented an end-to-end test with a home-made heterogeneous moving phantom and ionization chambers measurements. Robustly optimized plans with prescription doses of 6 Gy(RBE) were delivered in different dynamic conditions.
Both 4D robustly optimized plans reached the same target coverage (p = 0.56), while a statistically significant decrease of the homolateral lung dose was observed using the restricted approach (p < 0.0001). Plan recalculations within 15 days from the treatment simulation showed the same robustness of target D98% against interfractional variations (p = 0.48), with an average decrease of approximately 3 Gy(RBE). Phantom measurements confirmed the delivery accuracy of the restricted approach (mean dose deviations <5%). Higher deviations were found for ungated full 4DRO and larger motion amplitude.
The restricted approach combined with gating improved normal tissue sparing and was shown to be more robust to single fraction deliveries and large motion amplitude.
研究四维刚性优化（4DRO）对笔形束扫描质子治疗中肺癌患者剂量分布的影响。
对 20 例肺癌患者采用 2 种策略进行比较，在计划优化问题中，分别采用不同数量的重建 4DCT 呼吸相。在结合门控的限制方法中，仅考虑参考呼气末附近的 3 个相位，而不是整个呼吸周期。处方剂量为 60Gy(RBE)，共 10 个分次。采用 Wilcoxon 符号秩检验评估靶区覆盖率（D98%）和健康组织剂量。为评估对分次间解剖和呼吸变异的稳健性，在重新评估的 4DCT 上重新计算优化计划。为了比较两种策略对互作用效应的敏感性，我们使用自制的不均匀运动体模和电离室测量进行了端到端测试。在不同的动态条件下，对具有 6Gy(RBE)处方剂量的稳健优化计划进行了递送。
两种 4D 稳健优化计划均达到了相同的靶区覆盖率（p=0.56），而采用限制方法可显著降低同侧肺剂量（p<0.0001）。在治疗模拟后 15 天内重新计算计划，显示出对靶区 D98%的相同稳健性，不受分次间变异的影响（p=0.48），平均降低约 3Gy(RBE)。体模测量结果证实了限制方法的递药准确性（平均剂量偏差<5%）。对于无门控的全 4DRO 和较大的运动幅度，发现了更高的偏差。
结合门控的限制方法可改善正常组织的保护，并显示出对单次递送和较大运动幅度的稳健性更高。
