Center for Proton Therapy, Paul Scherrer Institute, Villigen, Switzerland.
Department of Physics, ETH Zurich, Zurich, Switzerland.
Med Phys. 2021 Jul;48(7):4017-4026. doi: 10.1002/mp.14933. Epub 2021 May 25.
The purpose of this work was to provide a flexible platform for FLASH research with protons by adapting a former clinical pencil beam scanning gantry to irradiations with ultra-high dose rates.
PSI Gantry 1 treated patients until December 2018. We optimized the beamline parameters to transport the 250 MeV beam extracted from the PSI COMET accelerator to the treatment room, maximizing the transmission of beam intensity to the sample. We characterized a dose monitor on the gantry to ensure good control of the dose, delivered in spot-scanning mode. We characterized the beam for different dose rates and field sizes for transmission irradiations. We explored scanning possibilities in order to enable conformal irradiations or transmission irradiations of large targets (with transverse scanning).
We achieved a transmission of 86% from the cyclotron to the treatment room. We reached a peak dose rate of 9000 Gy/s at 3 mm water equivalent depth, along the central axis of a single pencil beam. Field sizes of up to 5 × 5 mm were achieved for single-spot FLASH irradiations. Fast transverse scanning allowed to cover a field of 16 × 1.2 cm . With the use of a nozzle-mounted range shifter, we are able to span depths in water ranging from 19.6 to 37.9 cm. Various dose levels were delivered with precision within less than 1%.
We have realized a proton FLASH irradiation setup able to investigate continuously a wide dose rate spectrum, from 1 to 9000 Gy/s in single-spot irradiation as well as in the pencil beam scanning mode. As such, we have developed a versatile test bench for FLASH research.
本工作旨在通过将前临床笔形束扫描龙门架适配为超高剂量率的辐照，为质子 FLASH 研究提供一个灵活的平台。
PSI 龙门架 1 一直用于治疗患者，直至 2018 年 12 月。我们优化了束流线参数，以便将从 PSI COMET 加速器提取的 250 MeV 束传输到治疗室，最大限度地提高了束强度传输到样品的效率。我们对龙门架上的剂量监测器进行了特征描述，以确保在点扫描模式下实现良好的剂量控制。我们对不同剂量率和射野大小的束流进行了特征描述，以实现传输辐照。我们探索了扫描的可能性，以实现对大目标（横向扫描）的适形辐照或传输辐照。
我们实现了从回旋加速器到治疗室的 86%的传输效率。我们在 3 毫米水等效深度处，沿着单个笔形束的中心轴，达到了 9000 Gy/s 的峰值剂量率。单点 FLASH 辐照可实现 5×5 毫米的射野大小。快速横向扫描允许覆盖 16×1.2 厘米的场。使用安装在喷嘴上的射程移位器，我们能够在水中的深度范围从 19.6 厘米到 37.9 厘米。各种剂量水平的精度误差都在 1%以内。
我们已经实现了一个质子 FLASH 辐照设置，能够在单点辐照以及笔形束扫描模式下连续研究从 1 到 9000 Gy/s 的宽剂量率谱。因此，我们已经开发了一个用于 FLASH 研究的多功能测试平台。
