New York Proton Center, New York, New York, USA.
Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, New York, USA.
J Appl Clin Med Phys. 2024 Aug;25(8):e14400. doi: 10.1002/acm2.14400. Epub 2024 Jun 3.
Quality assurance (QA) for ultra-high dose rate (UHDR) irradiation is a crucial aspect in the emerging field of FLASH radiotherapy (FLASH-RT). This innovative treatment approach delivers radiation at UHDR, demanding careful adoption of QA protocols and procedures. A comprehensive understanding of beam properties and dosimetry consistency is vital to ensure the safe and effective delivery of FLASH-RT.
To develop a comprehensive pre-treatment QA program for cyclotron-based proton pencil beam scanning (PBS) FLASH-RT. Establish appropriate tolerances for QA items based on this study's outcomes and TG-224 recommendations.
A 250 MeV proton spot pattern was designed and implemented using UHDR with a 215nA nozzle beam current. The QA pattern that covers a central uniform field area, various spot spacings, spot delivery modes and scanning directions, and enabling the assessment of absolute, relative and temporal dosimetry QA parameters. A strip ionization chamber array (SICA) and an Advanced Markus chamber were utilized in conjunction with a 2 cm polyethylene slab and a range (R) verification wedge. The data have been monitored for over 3 months.
The relative dosimetries were compliant with TG-224. The variations of temporal dosimetry for scanning speed, spot dwell time, and spot transition time were within ± 1 mm/ms, ± 0.2 ms, and ± 0.2 ms, respectively. While the beam-to-beam absolute output on the same day reached up to 2.14%, the day-to-day variation was as high as 9.69%. High correlation between the absolute dose and dose rate fluctuations were identified. The dose rate of the central 5 × 5 cm field exhibited variations within 5% of the baseline value (155 Gy/s) during an experimental session.
A comprehensive QA program for FLASH-RT was developed and effectively assesses the performance of a UHDR delivery system. Establishing tolerances to unify standards and offering direction for future advancements in the evolving FLASH-RT field.
超高剂量率（UHDR）辐照的质量保证（QA）是 FLASH 放射治疗（FLASH-RT）这一新兴领域的关键环节。这种创新的治疗方法以 UHDR 提供辐射，需要仔细采用 QA 协议和程序。全面了解束特性和剂量一致性对于确保 FLASH-RT 的安全有效递送至关重要。
为基于回旋加速器的质子笔束扫描（PBS）FLASH-RT 开发全面的治疗前 QA 计划。根据本研究结果和 TG-224 建议，为 QA 项目确定适当的容差。
采用 215nA 喷嘴束流的 UHDR 设计并实施 250 MeV 质子点模式。QA 模式涵盖了一个中心均匀场区域、各种点间距、点传递模式和扫描方向，能够评估绝对、相对和时间剂量学 QA 参数。使用条带电离室阵列（SICA）和高级 Markus 室，结合 2cm 聚乙烯平板和一个范围（R）验证楔。数据已监测超过 3 个月。
相对剂量学符合 TG-224。扫描速度、点停留时间和点转换时间的时间剂量学变化分别在±1mm/ms、±0.2ms 和±0.2ms 以内。同一天的束流到束流绝对输出最高可达 2.14%，而每天的变化高达 9.69%。确定了绝对剂量和剂量率波动之间的高度相关性。在一个实验过程中，中央 5×5cm 场的剂量率在基线值（155Gy/s）的 5%以内波动。
为 FLASH-RT 开发了全面的 QA 计划，并有效地评估了 UHDR 递送系统的性能。建立容差以统一标准，并为不断发展的 FLASH-RT 领域的未来发展提供方向。
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