Department of Physics and Astronomy, University of Victoria, Victoria, British Columbia, Canada.
Medscint Inc., Quebec City, QC, Canada.
Med Phys. 2021 Nov;48(11):7399-7409. doi: 10.1002/mp.15234. Epub 2021 Sep 25.
To present an x-ray tube system capable of in vitro ultrahigh dose-rate (UHDR) irradiation of small < 0.3 mm samples and to characterize it by means of a plastic scintillation detector (PSD).
A conventional x-ray tube was modified for the delivery of short UHDR irradiations. A beam shutter system with a sample holder was designed and installed in a close proximity of an x-ray tube window to enable <1 s irradiations at UHDR. The dosimetry was performed with a small 0.5-mm long 0.5-mm in diameter PSD irradiated with 80, 100, and 120 kVp beams and beam currents of 1-37.5 mA. The PSD signal was recorded at frame rates of 20 and 50 fps for shutter exposure between 100 and 1125 ms. Irradiation reproducibility was studied with the PSD. The x-ray tube irradiation setup was modeled with Monte Carlo (MC) and dose on a surface of a phantom was also measured with films. The effect of dose delivery uncertainty to 300-μm spheroids due to positioning and spheroid size was evaluated.
MC simulations showed good agreement with PSD measurements acquired at both frame rates of 20 and 50 fps in terms of beam temporal profile. PSD-measured dose exhibited excellent linearity as a function of instantaneous dose rate from 3.1 to 118.0 Gy/s as well as shutter exposure time from 100 and 1125 ms for all investigated beam energies. PSD absorbed dose for the 80, 100, and 120 kVp beams agreed with MC simulations to within 5%. The total delivered doses ranged from 0.4 Gy for a 1-mA, 80 kVp beam, and 100 ms shutter exposure to 166.9 Gy for a 37.5-mA, 80 kVp beam, and a 1125 ms exposure. PSD irradiation reproducibility was < 0.5%. Simulated and measured dose fall off agreed and it was steep along the axis of the shutter slit (1%/0.1 mm) and with depth (2%/0.1 mm at 1-mm depth). Spheroid positioning uncertainty of 300 μm resulted in dose difference of < 3% for x and y shifts but up to 7% uncertainty for a z-shift parallel to the beam axis. A 16% difference in spheroid size resulted in <5% dose difference in spheroid absorbed dose.
We have presented a cost-effective x-ray tube-based system with a beam shutter designed for in vitro UHDR delivery and reaching dose rates of up to 118.0 Gy/s. The described shutter system can be easily implemented at other institutions, which might enable new researchers to investigate the radiobiology of UHDR irradiations in vitro.
介绍一种能够对小<0.3mm 的样品进行体外超高剂量率（UHDR）照射的 X 射线管系统，并使用塑料闪烁探测器（PSD）对其进行特性描述。
对常规 X 射线管进行了改造，以实现短时间 UHDR 照射。设计并安装了一个带有样品架的束快门系统，使其能够在 X 射线管窗口的近距离处进行<1 秒的 UHDR 照射。使用 0.5mm 长、0.5mm 直径的小 PSD 进行剂量测定，并用 80、100 和 120 kVp 射线和 1-37.5mA 的射线电流进行照射。PSD 信号在快门曝光时间为 100 和 1125ms 时以 20 和 50fps 的帧率进行记录。使用 PSD 研究了照射重现性。使用蒙特卡罗（MC）对 X 射线管照射装置进行建模，并使用胶片测量了模体表面的剂量。评估了由于定位和球体大小导致的 300μm 球体剂量传递不确定性的影响。
MC 模拟结果与在 20 和 50fps 两种帧率下通过 PSD 测量获得的束时间分布非常吻合。PSD 测量的剂量显示出很好的线性关系，瞬时剂量率范围为 3.1 至 118.0Gy/s，快门曝光时间范围为 100 和 1125ms，适用于所有研究的射线能量。80、100 和 120kVp 射线的 PSD 吸收剂量与 MC 模拟结果的偏差在 5%以内。总输送剂量范围从 1mA、80kVp 射线和 100ms 快门曝光的 0.4Gy 到 37.5mA、80kVp 射线和 1125ms 曝光的 166.9Gy。PSD 照射重现性<0.5%。模拟和测量的剂量衰减一致，沿快门狭缝的轴（1%/0.1mm）和深度（在 1mm 深度处为 2%/0.1mm）都很陡峭。球体定位不确定性为 300μm 时，x 和 y 方向的剂量差异<3%，而平行于束轴的 z 方向的剂量不确定性高达 7%。球体大小相差 16%，则球体吸收剂量的差异<5%。
我们提出了一种具有成本效益的基于 X 射线管的系统，该系统带有一个设计用于体外 UHDR 输送的束快门，能够达到高达 118.0Gy/s 的剂量率。所描述的快门系统可以很容易地在其他机构实施，这可能使新的研究人员能够在体外研究 UHDR 照射的放射生物学。
