Department of Radiation Oncology and Molecular Radiation Sciences, Faculty of Medicine, Johns Hopkins University, United States of America.
Department of Mechanical Engineering, Whiting School of Engineering, Johns Hopkins University, United States of America.
Phys Med Biol. 2021 Apr 23;66(9). doi: 10.1088/1361-6560/abf2fa.
FLASH irradiation has been shown to reduce significantly normal tissue toxicity compared to conventional irradiation, while maintaining tumor control probability at similar level. Clinical translation of FLASH irradiation necessitates comprehensive laboratory studies to elucidate biological effects as well as pertinent technological and physical requirements. At present, FLASH research employs complex accelerator technologies of limited accessibilities. Here, we study the feasibility of a novel self-shielded x-ray irradiation cabinet system, as an enabling technology to enhance the preclinical research capabilities. The proposed system employs two commercially available high capacity 150 kVp fluoroscopy x-ray sources with rotating anode technology in a parallel-opposed arrangement. Simulation was performed with the GEANT4 Monte-Carlo platform. Simulated dosimetric properties of the x-ray beam for both FLASH and conventional dose-rate irradiations were characterized. Dose and dose rate from a single kV x-ray fluoroscopy source in solid water phantom were verified with measurements using Gafchromic films. The parallel-opposed x-ray sources can deliver over 50 Gy doses to a 20 mm thick water equivalent medium at ultrahigh dose-rates of 40-240 Gy s. A uniform depth-dose rate (±5%) is achieved over 8-12 mm in the central region of the phantom. Mirrored beams minimize heel effect of the source and achieve reasonable cross-beam uniformity (±3%). Conventional dose-rate irradiation (≤0.1 Gy s) can also be achieved by reducing the tube current and increasing the distance between the phantom and tubes. The rotating anode x-ray source can be used to deliver both FLASH and conventional dose-rate irradiations with the field dimensions well suitable for small animal and cell-culture irradiations. For FLASH irradiation using parallel-opposed sources, entrance and exit doses can be higher by 30% than the dose at the phantom center. Beam angling can be employed to minimize the high surface doses. Our proposed system is amendable to self-shielding and enhance research in regular laboratory setting.
FLASH 照射已被证明能显著降低正常组织毒性，同时保持类似水平的肿瘤控制概率。FLASH 照射的临床转化需要全面的实验室研究来阐明生物学效应以及相关的技术和物理要求。目前，FLASH 研究采用了复杂的、可及性有限的加速器技术。在这里，我们研究了一种新型的自屏蔽 X 射线照射箱系统的可行性，该系统是增强临床前研究能力的一项使能技术。所提出的系统采用了两个商用的高容量 150 kVp 透视 X 射线源，采用旋转阳极技术，呈平行对置排列。模拟使用了 GEANT4 蒙特卡罗平台。对 FLASH 和常规剂量率照射的 X 射线束的模拟剂量学特性进行了表征。使用 Gafchromic 胶片进行了测量，验证了在固体水模体中来自单个千伏 X 射线透视源的剂量和剂量率。平行对置的 X 射线源可以在超高剂量率（40-240 Gy s）下向 20 毫米厚的水等效介质输送超过 50 Gy 的剂量。在模体中心区域 8-12 毫米的深度内，实现了均匀的深度剂量率（±5%）。镜像光束最小化了源的脚跟效应，并实现了合理的跨束均匀性（±3%）。通过降低管电流和增加模体与管之间的距离，也可以实现常规剂量率照射（≤0.1 Gy s）。旋转阳极 X 射线源可用于提供 FLASH 和常规剂量率照射，其射野尺寸非常适合小动物和细胞培养照射。对于平行对置源的 FLASH 照射，入口和出口剂量比模体中心的剂量高 30%。可以采用束角来最小化表面高剂量。我们提出的系统易于进行自屏蔽，并能在常规实验室环境中增强研究。
