Miles Devin, Sforza Daniel, Wong John, Rezaee Mohammad
Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
Med Phys. 2024 Feb;51(2):1474-1483. doi: 10.1002/mp.16609. Epub 2023 Jul 17.
Most current research toward ultra-high dose rate (FLASH) radiation is conducted with advanced proton and electron accelerators, which are of limited accessibility to basic laboratory research. An economical alternative to charged particle accelerators is to employ high-capacity rotating anode x-ray tubes to produce kilovoltage x-rays at FLASH dose rates at short source-to-surface distances (SSD). This work describes a comprehensive dosimetric evaluation of a rotating anode x-ray tube for potential application in laboratory FLASH study.
A commercially available high-capacity fluoroscopy x-ray tube with 75 kW input power was implemented as a potential FLASH irradiator. Radiochromic EBT3 film and thermoluminescent dosimeters (TLDs) were used to investigate the effects of SSD and field size on dose rates and depth-dose characteristics in kV-compatible solid water phantoms. Custom 3D printed accessories were developed to enable reproducible phantom setup at very short SSD. Open and collimated radiation fields were assessed.
Despite the lower x-ray energy and short SSD used, FLASH dose rates above 40 Gy/s were achieved for targets up to 10-mm depth in solid water. Maximum surface dose rates of 96 Gy/s were measured in the open field at 47 mm SSD. A non-uniform high-to-low dose gradient was observed in the planar dose distribution, characteristic of anode heel effects. With added collimation, beams up to 10-mm diameter with reasonable uniformity can be produced. Typical 80%-20% penumbra in the collimated x-ray FLASH beams were less than 1 mm at 5-mm depth in phantom. Ramp-up times at the maximum input current were less than 1 ms.
Our dosimetric characterization demonstrates that rotating anode x-ray tube technology is capable of producing radiation beams in support of preclinical FLASH radiobiology research.
目前大多数关于超高剂量率（FLASH）辐射的研究是使用先进的质子和电子加速器进行的，而这些加速器在基础实验室研究中的可及性有限。一种替代带电粒子加速器的经济方法是使用高容量旋转阳极X射线管，以在短源皮距（SSD）下产生FLASH剂量率的千伏X射线。这项工作描述了对旋转阳极X射线管在实验室FLASH研究中的潜在应用进行的全面剂量学评估。
使用一台输入功率为75kW的市售高容量荧光透视X射线管作为潜在的FLASH辐照器。使用放射变色EBT3薄膜和热释光剂量计（TLD）来研究SSD和射野大小对千伏兼容固体水模体中剂量率和深度剂量特性的影响。开发了定制的3D打印配件，以在非常短的SSD下实现可重复的模体设置。评估了开放和准直辐射野。
尽管使用的X射线能量较低且SSD较短，但在固体水中深度达10mm的靶区实现了高于40Gy/s的FLASH剂量率。在SSD为47mm的开放野中测得的最大表面剂量率为96Gy/s。在平面剂量分布中观察到从高到低的不均匀剂量梯度，这是阳极足跟效应的特征。通过增加准直，可以产生直径达10mm且均匀性合理的射束。在模体中5mm深度处，准直X射线FLASH射束的典型80%-20%半值层小于1mm。在最大输入电流时的上升时间小于1ms。
我们的剂量学表征表明，旋转阳极X射线管技术能够产生辐射束，以支持临床前FLASH放射生物学研究。
