Schönfeld Andreas A, Hildreth Jeff, Bourgouin Alexandra, Flatten Veronika, Kozelka Jakub, Simon William, Schüller Andreas
Research and Development, Sun Nuclear Corp., Melbourne, Florida, USA.
Dosimetry for Radiotherapy, Physikalisch-Technische Bundesanstalt, Braunschweig, 38116, Germany.
Med Phys. 2025 Mar;52(3):1845-1857. doi: 10.1002/mp.17573. Epub 2024 Dec 17.
FLASH radiotherapy is an emerging treatment modality using ultra-high dose rate beams. Much effort has been made to develop suitable dosimeters for reference dosimetry, yet the spatial beam characteristics must also be characterized to enable computerized treatment planning, as well as quality control and service of a treatment delivery device. In conventional radiation therapy, this is commonly achieved by beam profile scans in a water phantom using a point detector. In ultra-high dose rate beams, the delivered dose needed for a set of beam profile scans may exceed the regulatory dose limit specified for a typical treatment room, or degrade components of the scanning system and scanning detector. Point detector scans also cannot quantify the pulse-to-pulse stability of a beam profile. Detector arrays can overcome these challenges, but to date, no detector arrays suitable for ultra-high dose rate beams are commercially available.
The study presents the development and characterization of a two-dimensional detector array for measuring pulse-resolved spatial fluence distributions in real-time and temporal structure of intra-pulse dose rate of ultra-high pulsed dose rate (UHPDR) electron beams used in FLASH radiotherapy.
The performance of the SunPoint 1 diode was evaluated by measuring the response of the EDGE Detector in a 20 MeV UHPDR electron beam with a dose per pulse of 0.04 Gy - 6 Gy at a pulse duration of 1 µs or 1.9 µs, and instantaneous dose rates of 0.040 - 3.2 MGy·s. Based on the findings regarding a suitable signal acquisition technique, a PROFILER 2 detector array made of SunPoint 1 diodes was then modified by minimizing trace resistance, applying a reverse bias, and implementing an RC component to each diode to optimize the transfer of the collected charge during a pulse. The resultant "FLASH Profiler" was then tested in the same UHPDR electron beam.
The FLASH Profiler exhibited a linear response within ± 3% deviation over the investigated dose per pulse range. The FLASH Profiler array showed good agreement with the absolute dose measured using a flashDiamond point detector and an integrating current transformer for dose-per-pulse values of up to 6 Gy. The FLASH Profiler was able to measure lateral beam profiles in real-time and on a single-pulse basis. The ability to capture and display the profiles during steering of UHPDR beams was demonstrated. The SunPoint 1 diode was able to measure the pulse duration and the intra-pulse dose rate with a time resolution of 4 ns.
The FLASH Profiler could be used for characterizing UHPDR electron beams and facilitating quality control and beam steering service of electron FLASH irradiators.
闪疗是一种使用超高剂量率射束的新兴治疗方式。人们已付出诸多努力来开发适用于参考剂量测定的剂量仪，但还必须对射束的空间特性进行表征，以实现计算机化治疗计划以及治疗输送设备的质量控制和服务。在传统放射治疗中，这通常通过在水模体中使用点探测器进行射束剖面扫描来实现。在超高剂量率射束中，一组射束剖面扫描所需的输送剂量可能超过典型治疗室规定的监管剂量限值，或者使扫描系统和扫描探测器的部件退化。点探测器扫描也无法量化射束剖面的脉冲间稳定性。探测器阵列可以克服这些挑战，但迄今为止，尚无适用于超高剂量率射束的商用探测器阵列。
本研究展示了一种二维探测器阵列的开发与表征，该阵列用于实时测量脉冲分辨的空间注量分布以及闪疗中使用的超高脉冲剂量率（UHPDR）电子束的脉冲内剂量率的时间结构。
通过在20 MeV的UHPDR电子束中测量EDGE探测器的响应来评估SunPoint 1二极管的性能，该电子束的脉冲持续时间为1 μs或1.9 μs，每个脉冲的剂量为0.04 Gy - 6 Gy，瞬时剂量率为0.040 - 3.2 MGy·s。基于关于合适信号采集技术的研究结果，然后对由SunPoint 1二极管制成的PROFILER 2探测器阵列进行改进，方法是最小化走线电阻、施加反向偏置并在每个二极管上设置一个RC元件，以优化脉冲期间收集电荷的传输。然后在相同的UHPDR电子束中对所得的“闪疗剖面仪”进行测试。
闪疗剖面仪在研究的每个脉冲剂量范围内，偏差在±3% 以内呈现线性响应。对于高达6 Gy的每个脉冲剂量值，闪疗剖面仪阵列与使用闪晶点探测器和积分电流互感器测量的绝对剂量显示出良好的一致性。闪疗剖面仪能够实时且基于单脉冲测量横向射束剖面。展示了在UHPDR射束转向期间捕获和显示剖面的能力。SunPoint 1二极管能够以4 ns的时间分辨率测量脉冲持续时间和脉冲内剂量率。
闪疗剖面仪可用于表征UHPDR电子束，并有助于电子闪疗照射器的质量控制和射束转向服务。
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