Thayer School of Engineering, Dartmouth College, Hanover NH 03755, United States of America.
Department of Medicine, Radiation Oncology, Geisel School of Medicine, Dartmouth College, Hanover NH 03755 United States of America.
Phys Med Biol. 2021 Jun 30;66(13). doi: 10.1088/1361-6560/ac0390.
In this study, spatio-temporal beam profiling for electron ultra-high dose rate (UHDR; >40 Gy s) radiation via Cherenkov emission and radioluminescence imaging was investigated using intensified complementary metal-oxide-semiconductor cameras.The cameras, gated to FLASH optimized linear accelerator pulses, imaged radioluminescence and Cherenkov emission incited by single pulses of a UHDR (>40 Gy s) 10 MeV electron beam delivered to the isocenter. Surface dosimetry was investigated via imaging Cherenkov emission or scintillation from a solid water phantom or GdOS:Tb screen positioned on top of the phantom, respectively. Projected depth-dose profiles were imaged from a tank filled with water (Cherenkov emission) and a 1 g lquinine sulfate solution (scintillation). These optical results were compared with projected lateral dose profiles measured by Gafchromic film at different depths, including the surface.The per-pulse beam output from Cherenkov imaging agreed with the photomultiplier tube Cherenkov output to within 3% after about the first five to seven ramp-up pulses. Cherenkov emission and scintillation were linear with dose ( = 0.987 and 0.995, respectively) and independent of dose rate from ∼50 to 300 Gy s(0.18-0.91 Gy/pulse). The surface dose distribution from film agreed better with scintillation than with Cherenkov emission imaging (3%/3 mm gamma pass rates of 98.9% and 88.8%, respectively). Using a 450 nm bandpass filter, the quinine sulfate-based water imaging of the projected depth optical profiles agreed with the projected film dose to within 5%.The agreement of surface dosimetry using scintillation screen imaging and Gafchromic film suggests it can verify the consistency of daily beam quality assurance parameters with an accuracy of around 2% or 2 mm. Cherenkov-based surface dosimetry was affected by the target's optical properties, prompting additional calibration. In projected depth-dose profiling, scintillation imaging via spectral suppression of Cherenkov emission provided the best match to film. Both camera-based imaging modalities resolved dose from single UHDR beam pulses of up to 60 Hz repetition rate and 1 mm spatial resolution.
本研究通过切伦科夫发射和光致发光成像，对电子超高剂量率（UHDR；>40 Gy s）辐射的时空束剖面进行了研究，使用增强型互补金属氧化物半导体（CMOS）相机。这些相机与FLASH 优化的线性加速器脉冲门控，对单次 UHDR（>40 Gy s）10 MeV 电子束照射到等中心时激发的光致发光和切伦科夫发射进行成像。通过分别在体模顶部放置固体水或 GdOS：Tb 屏幕，对表面剂量进行了成像，以测量 Cherenkov 发射或闪烁。用水（切伦科夫发射）和 1 g l 硫酸奎宁溶液（闪烁）填充的水箱的投影深度剂量曲线通过光成像进行了拍摄。这些光学结果与不同深度的 Gafchromic 胶片测量的投影横向剂量曲线进行了比较，包括表面。Cherenkov 成像的逐脉冲束输出与光电倍增管 Cherenkov 输出的差异在大约前五个到七个斜坡上升脉冲后在 3%以内。Cherenkov 发射和闪烁与剂量呈线性关系（分别为 0.987 和 0.995），并且在 50 至 300 Gy s（0.18-0.91 Gy/pulse）的剂量率范围内独立。胶片的表面剂量分布与闪烁相比，与 Cherenkov 成像更吻合（3%/3 mm 伽马通过率分别为 98.9%和 88.8%）。使用 450nm 带通滤波器，基于硫酸奎宁的水的投影深度光学轮廓的成像与投影胶片剂量的一致性在 5%以内。闪烁屏成像和 Gafchromic 胶片的表面剂量测量的一致性表明，它可以以 2%或 2mm 的精度验证日常束质量保证参数的一致性。基于 Cherenkov 的表面剂量测量受到目标光学特性的影响，因此需要进行额外的校准。在投影深度剂量分布中，通过抑制 Cherenkov 发射的光谱抑制进行闪烁成像，可与胶片达到最佳匹配。这两种基于相机的成像方式都可以解析高达 60Hz 重复率和 1mm 空间分辨率的单次 UHDR 光束脉冲的剂量。
