Wei Shouyi, Lin Haibo, Choi J Isabelle, Simone Charles B, Kang Minglei
New York Proton Center, New York, NY 10035, USA.
Cancers (Basel). 2021 Nov 18;13(22):5790. doi: 10.3390/cancers13225790.
While transmission proton beams have been demonstrated to achieve ultra-high dose rate FLASH therapy delivery, they are unable to spare normal tissues distal to the target. This study aims to compare FLASH treatment planning using single energy Bragg peak proton beams versus transmission proton beams in lung tumors and to evaluate Bragg peak plan optimization, characterize plan quality, and quantify organ-at-risk (OAR) sparing.
Both Bragg peak and transmission plans were optimized using an in-house platform for 10 consecutive lung patients previously treated with proton stereotactic body radiation therapy (SBRT). To bring the dose rate up to the FLASH-RT threshold, Bragg peak plans with a minimum MU/spot of 1200 and transmission plans with a minimum MU/spot of 400 were developed. Two common prescriptions, 34 Gy in 1 fraction and 54 Gy in 3 fractions, were studied with the same beam arrangement for both Bragg peak and transmission plans ( = 40 plans). RTOG 0915 dosimetry metrics and dose rate metrics based on different dose rate calculations, including average dose rate (ADR), dose-averaged dose rate (DADR), and dose threshold dose rate (DTDR), were investigated. We then evaluated the effect of beam angular optimization on the Bragg peak plans to explore the potential for superior OAR sparing.
Bragg peak plans significantly reduced doses to several OAR dose parameters, including lung V and V by 32.0% ( < 0.01) and 30.4% ( < 0.01) for 34Gy/fx plans, respectively; and by 40.8% ( < 0.01) and 41.2% ( < 0.01) for 18Gy/fx plans, respectively, compared with transmission plans. Bragg peak plans have ~3% less in DADR and ~10% differences in mean OARs in DTDR and DADR relative to transmission plans due to the larger portion of lower dose regions of Bragg peak plans. With angular optimization, optimized Bragg peak plans can further reduce the lung V by 20.7% ( < 0.01) and V by 19.7% ( < 0.01) compared with Bragg peak plans without angular optimization while achieving a similar 3D dose rate distribution.
The single-energy Bragg peak plans achieve superior dosimetry performances in OARs to transmission plans with comparable dose rate performances for lung cancer FLASH therapy. Beam angle optimization can further improve the OAR dosimetry parameters with similar 3D FLASH dose rate coverage.
虽然已证明传输质子束可实现超高剂量率的FLASH治疗，但它们无法保护靶区远端的正常组织。本研究旨在比较使用单能布拉格峰质子束与传输质子束对肺部肿瘤进行FLASH治疗计划，并评估布拉格峰计划的优化情况，表征计划质量，以及量化危及器官（OAR）的保护情况。
使用内部平台对10例先前接受过质子立体定向体部放射治疗（SBRT）的连续肺部患者的布拉格峰计划和传输计划进行了优化。为了将剂量率提高到FLASH-RT阈值，制定了最小MU/点为1200的布拉格峰计划和最小MU/点为400的传输计划。研究了两种常见的处方，即1次分割给予34 Gy和3次分割给予54 Gy，布拉格峰计划和传输计划采用相同的射束排列（共40个计划）。研究了基于不同剂量率计算的RTOG 0915剂量学指标和剂量率指标，包括平均剂量率（ADR）、剂量平均剂量率（DADR）和剂量阈值剂量率（DTDR）。然后，我们评估了射束角度优化对布拉格峰计划的影响，以探索更好地保护OAR的潜力。
与传输计划相比，布拉格峰计划显著降低了多个OAR剂量参数的剂量，对于34 Gy/fx计划，肺部V和V分别降低了32.0%（P<0.01）和30.4%（P<0.01）；对于18 Gy/fx计划，分别降低了40.8%（P<0.01）和41.2%（P<0.01）。由于布拉格峰计划中低剂量区域的比例较大，其DADR比传输计划低约3%，DTDR和DADR中的平均OAR差异约为10%。通过角度优化，与未进行角度优化的布拉格峰计划相比，优化后的布拉格峰计划可使肺部V进一步降低20.7%（P<0.01），V降低19.7%（P<0.01），同时实现相似的三维剂量率分布。
对于肺癌FLASH治疗，单能布拉格峰计划在OAR方面的剂量学性能优于传输计划，且剂量率性能相当。射束角度优化可在相似的三维FLASH剂量率覆盖下进一步改善OAR剂量学参数。
