[论文解读] Feasibility Study of Hybrid Inverse Planning with Transmission Beams and Single-energy Spread-out Bragg Peaks for Proton Flash Radiotherapy

Chaoqiong Ma, Xiaofeng Yang+7 more|arXiv (Cornell University)|Sep 14, 2022

Advanced Radiotherapy Techniques被引用 4

一句话总结

本研究提出一种混合逆向质子放射治疗计划方法，结合传输射野（TBs）与单能布拉格峰展宽（SESOBPs），以在质子FLASH放射治疗中更好地保护正常组织。通过使用射野范围移位器和条纹形滤线器生成SESOBPs，并优化逐野射野选择与权重分配，该方法在保持靶区均匀性与FLASH剂量率输送的前提下，使脊髓D1.2cc降低41%，并改善了肺部组织的保护效果，相比仅使用TB的计划更具优势。

ABSTRACT

Ultra-high dose rate (FLASH) proton planning with only transmission beams (TBs) has limitations in normal tissue sparing. The single-energy spread-out Bragg peaks (SESOBPs) of FLASH dose rate have been demonstrated feasible for proton FLASH planning. A hybrid inverse optimization method was developed to combine the TBs and SESOBPs (TB-SESOBP) for FLASH planning. The SESOBPs were generated from spreading out the BPs by pre-designed general bar ridge filters and placed at the central target by range shifters to obtain a uniform dose within the target. The SESOBPs and TBs were fully sampled field-by-field allowing automatic spot selection and weighting in the optimization process. The TB-SESOBP plans were validated in comparison with the TB only (TB-only) plans and the plans with the combination of TBs and BPs (TB-BP) regarding 3D dose and dose rate distributions for five lung cases. Comparing to the TB-only plans, the mean spinal cord D1.2cc drastically reduced 41%, the mean lung V7Gy and V7.4Gy moderately reduced by up to 17% and the target dose homogeneity slightly increased in the TB-SESOBP plans. Comparable dose homogeneity was achieved in both TB-SESOBP and TB-BP plans. Besides, prominent improvements were achieved in lung sparing for the cases of relatively large targets by the TB-SESOBP plans comparing to the TB-BP plans. The targets were fully covered with the FLASH dose rate in all the three plans. For the OARs, V40Gy/s = 100% was achieved by the TB-only plans while V40Gy/s > 85% was obtained by the other two plans. We have demonstrated that the hybrid TB-SESOBP planning was feasible to achieve FLASH dose rate for proton therapy. The hybrid TB-SESOBP planning has great potential in improving OAR sparing while maintaining high target dose homogeneity, and can be potentially implemented for adaptive radiotherapy.

研究动机与目标

• 为解决仅使用传输射野（TB-only）FLASH质子放射治疗在保护正常组织方面的局限性。
• 研究将单能布拉格峰展宽（SESOBPs）与传输射野结合的可行性，以实现对危及器官（OAR）的更好保护。
• 开发一种混合逆向优化框架，实现TB与SESOBPs的自动射野选择与权重分配。
• 通过剂量分布与剂量率输送性能，将该混合方法与仅使用TB及TB-BP（射野对）计划进行验证。
• 评估该混合方法在临床环境中用于自适应放疗的潜力。

提出的方法

• 采用传输射野（TBs）与通过预先设计的条纹形滤线器及射野范围移位器生成的SESOBPs，以实现靶区的均匀覆盖。
• 使用包含TB与SESOBPs的完整逐野采样进行逆向强度调控质子治疗（IMPT）优化。
• 通过逆向优化实现自动点射野选择与射野权重分配，确保最优剂量分布。
• 应用射野范围移位器，将SESOBPs定位在靶区中心区域，以实现展宽布拉格峰特性。
• 使用五个临床肺部肿瘤病例，结合3D剂量与剂量率分析，验证该混合方法。
• 采用标准剂量学指标与FLASH剂量率标准，将TB-SESOBP计划与仅使用TB及TB-BP计划进行对比。

实验结果

研究问题

• RQ1 与仅使用TB的计划相比，将SESOBPs与传输射野结合是否能改善质子FLASH放射治疗中正常组织的保护效果？
• RQ2 在靶区剂量均匀性与OAR保护方面，混合TB-SESOBP方法与传统TB-BP计划相比表现如何？
• RQ3 该混合方法在靶区与OAR中多大程度上能维持FLASH剂量率（≥40 Gy/s）？
• RQ4 该混合TB-SESOBP方法在临床实施中是否可行，特别是在自适应放疗场景下？
• RQ5 在FLASH质子治疗背景下，SESOBPs相较于传统布拉格峰有何剂量学优势？

主要发现

• 与仅使用TB的计划相比，TB-SESOBP计划使脊髓D1.2cc的平均剂量降低了41%，显著改善了脊髓保护效果。
• 与仅使用TB的计划相比，TB-SESOBP计划中肺部V7Gy与V7.4Gy分别降低了最多17%，表明肺部组织保护效果更优。
• 与仅使用TB的计划相比，TB-SESOBP计划的靶区剂量均匀性略有改善，且与TB-BP计划的均匀性相当。
• 对于靶区相对较大的病例，TB-SESOBP计划在肺部保护方面优于TB-BP计划。
• 三种计划（仅使用TB、TB-BP、TB-SESOBP）在靶区均实现了V40Gy/s = 100%，证实了完整的FLASH剂量率覆盖。
• TB-SESOBP方法在OAR中保持了V40Gy/s > 85%，表明在关键结构中实现了稳健的FLASH剂量率输送。