Guo Lixiang, Zhou Banghao, Tsai Yi-Chun, Jiang Kai, Iakovenko Viktor, Wang Ken Kang-Hsin
Biomedical Imaging and Radiation Technology Laboratory (BIRTLab), Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, Texas, USA.
Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, Texas, USA.
Med Phys. 2025 Oct;52(10):e70006. doi: 10.1002/mp.70006.
The normal tissue sparing effect of ultra-high dose rate irradiation (≥40 Gy/s, UHDR), as compared to conventional dose rate (CONV), has attracted significant research interest for FLASH radiotherapy (RT). Accurate, dose rate independent, fast-responding dosimeters capable of resolving the spatiotemporal characteristics of UHDR beams are urgently needed to facilitate FLASH research and support its clinical translation. Tissue-equivalent scintillators, with millimeter-level spatial resolution and millisecond-level temporal resolution, possess these required characteristics and show strong potential for use in UHDR dosimetry.
We investigated the performance of the HYPERSCINT RP-FLASH scintillator system at up to 1000 Hz sampling frequency (f) for UHDR electron beam dosimetry.
The scintillator was exposed to CONV and UHDR electron irradiation using a LINAC-based FLASH platform. Its spectral characteristics were delineated with a four-component calibration, followed by a signal-to-dose calibration using 18 MeV CONV electron beam. The dose linearity and dosimetric accuracy in response to CONV and UHDR irradiation at 1 and 1000 Hz f were quantified against ion chamber and EBT-XD film measurements. The response of the scintillator system was investigated as a function of beam energy (6 and 18 MeV), field size (2 × 2 to 25 × 25 cm), dose per pulse (DPP, 0.8-2.3 Gy/pulse), and pulse repetition frequency (PRF, 30-180 Hz). Relative signal sensitivity was quantified against accumulated dose to account for the scintillator's radiation degradation. Pulse-resolved dose measurements at 18 MeV UHDR, obtained using the scintillator with 1000 Hz f for a train of 10 pulses at 180 Hz PRF, were validated with a PMT-fiber optic scattered radiation detector.
The scintillator system at 1 Hz f demonstrated high accuracy in dose measurements, remaining within 0.5% of ion chamber measurements over the dose range of 0.1-35 Gy under CONV irradiation. For the UHDR irradiation, the scintillator showed <3% dose error compared to film measurements up to 40 Gy at 1000 Hz f. Its response was found to be minimally dependent on energy, field size, and PRF. The scintillator under-responded by ∼4% over the 0.8-2.3 Gy/pulse range, although the dose difference relative to film remained within 2%. The radiation degradation of the scintillation detector followed a 2-order polynomial fit between 0 and 10 kGy, and a linear fit with a slope of -2.6%/kGy in the range of 0-2 kGy. The pulse-resolved dose measured by the scintillator was verified to be within 3% accuracy when compared to the measurements obtained using the PMT-fiber optic detector.
With routine dose calibration to account for radiation induced degradation, the fast-responding scintillator system can accurately provide millisecond-resolved inter-pulse measurements for electron beams at conventional and ultra-high dose rates, with minimal dependence on beam parameters. This suggests that the HYPERSCINT RP-FLASH scintillator system could serve as a detector of choice for electron FLASH research.
与传统剂量率（CONV）相比，超高剂量率照射（≥40 Gy/s，UHDR）的正常组织保护效应引起了闪疗（RT）研究的极大兴趣。迫切需要精确的、与剂量率无关的、快速响应的剂量计，以解析UHDR束流的时空特性，从而促进闪疗研究并支持其临床转化。具有毫米级空间分辨率和毫秒级时间分辨率的组织等效闪烁体具备这些所需特性，在UHDR剂量测定中显示出强大的应用潜力。
我们研究了HYPERSCINT RP-FLASH闪烁体系统在高达1000 Hz采样频率（f）下用于UHDR电子束剂量测定的性能。
使用基于直线加速器的闪疗平台，使闪烁体接受CONV和UHDR电子照射。通过四分量校准描绘其光谱特性，随后使用18 MeV CONV电子束进行信号与剂量校准。在1 Hz和1000 Hz f下，针对CONV和UHDR照射，将闪烁体系统的剂量线性和剂量测定准确性与电离室和EBT-XD胶片测量结果进行对比量化。研究闪烁体系统的响应随束流能量（6 MeV和18 MeV）、射野大小（2×2至25×25 cm）、每脉冲剂量（DPP，0.8 - 2.3 Gy/脉冲）和脉冲重复频率（PRF，30 - 180 Hz）的变化情况。针对累积剂量量化相对信号灵敏度，以考虑闪烁体的辐射降解。使用1000 Hz f的闪烁体在180 Hz PRF下对10个脉冲序列进行18 MeV UHDR脉冲分辨剂量测量，并通过光电倍增管 - 光纤散射辐射探测器进行验证。
1 Hz f下的闪烁体系统在剂量测量中显示出高精度，在CONV照射下0.1 - 35 Gy剂量范围内，测量结果与电离室测量结果的偏差保持在0.5%以内。对于UHDR照射，在1000 Hz f下，剂量高达40 Gy时，与胶片测量相比，闪烁体的剂量误差小于3%。发现其响应对能量、射野大小和PRF的依赖性最小。在0.8 - 2.3 Gy/脉冲范围内，闪烁体响应低约4%，尽管相对于胶片的剂量差异仍在2%以内。闪烁探测器的辐射降解在0至10 kGy之间遵循二阶多项式拟合，在0至2 kGy范围内遵循斜率为 -2.6%/kGy的线性拟合。与使用光电倍增管 - 光纤探测器获得的测量结果相比，闪烁体测量的脉冲分辨剂量经验证准确性在3%以内。
通过常规剂量校准以考虑辐射诱导的降解，快速响应的闪烁体系统能够以最小的束流参数依赖性，准确地为传统和超高剂量率电子束提供毫秒级分辨的脉冲间测量。这表明HYPERSCINT RP-FLASH闪烁体系统可作为电子闪疗研究的首选探测器。
