Orthovoltage X-Ray Irradiator for Preclinical FLASH Studies

Abstract

Flash radiotherapy, the delivery of high radiation dose (> 10 Gy) at ultrahigh dose rates (> 37 Gy/s), has been shown to reduce significantly normal tissue toxicity compared to conventional irradiation, while maintaining tumor control probability at similar level. Great excitement has since ensued about the transformative potential of FLASH radiotherapy. At present, important 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 of the radiation research community.The proposed system employs two commercially available high capacity 150 kVp fluoroscopy x-ray sources, RAD-44 or G-1592 tubes, with rotating anode technology in a parallel-opposed arrangement. Simulation was performed using a simulation toolkit. Simulated dosimetric properties of the x-ray beam for both FLASH and conventional dose-rate irradiations were characterized in terms of output, uniformity and symmetry as a function of SSD, beam current, exposure time, and external filters. Dose and dose rate from a single kV x-ray fluoroscopy source at various depths in solid water phantom were verified with measurements using radiographic films.The parallel-opposed x-ray sources can deliver doses up to 67 Gy to a 20-mm thick water equivalent medium at FLASH dose-rates of 40 - 240 Gy/s. A uniform depth dose rate within ± 5% deviation is achieved over 8-12 mm in central region of the phantom. 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. Either the RAD-44 or G-1592 x-ray source can be used to deliver FLASH and conventional dose-rate irradiations with the field larger than 25 mm and up to 200 mm in length, respectively. These field dimensions are well suitable for small animal and cell culture irradiations. For FLASH irradiation using parallel-opposed source arrangement, entrance and exit doses can be increased by 30% compared to the dose at the phantom center. Beam angling can be employed to reduce the high surface doses by minimizing the beams overlap at the phantom surfaces. For a 10 × 10 mm2 field, for example, 26degree beam angle from vertical axis reduces the entrance dose by 39%, while maintaining FLASH dose rate of 118 Gy/s spanning in 8 mm thickness.It is feasible to achieve FLASH dose rate irradiation with kV x-rays using rotating anode x-ray sources in the parallel-opposed arrangement. The system is amendable to self-shielding and readily deployable. Availability of both FLASH and conventional dose rate irradiations in the same platform enables effective comparative research. A cabinet FLASH irradiation system will greatly enhance research in the regular laboratory setting to elucidate the important biological mechanism of the FLASH effect.