Purpose: Current research toward ultra-high dose rate radiotherapy (FLASH) is predominantly performed at clinic-oriented centers with advanced proton or electron accelerators. However, laboratory radiobiology research relies on standalone x-ray irradiators with stationary-anode technology, which are unsuitable for FLASH due to the immense power and heat loading requirements. Here we innovate the use of high-capacity rotating-anode x-ray tubes for laboratory FLASH research and present the initial dosimetric characterization of a FLASH-capable rotating-anode system.
Methods: A high-capacity rotating-anode x-ray tube was installed in our lab with a 75kW generator, operating at 150kVp with 0.025mm Cu added filtration. Calibrated EBT3 film was irradiated at varying depths in kV solid water to measure output, beam profiles, and percent-depth-dose parameters at 46mm source-to-surface distance (SSD). Additional film measurements were acquired at extended SSD (66mm) to confirm output linearity with tube current and exposure time.
Results: At the maximum current, surface dose rates at 46mm SSD range from 81 to 34 Gy/s across the 20x20mm^2 field due to anode heel effects. A useful beam for preclinical research was defined as the cathode-half of the field (10x20mm^2), with an average dose rate of 77.3±1.9 Gy/s and maximum deliverable dose of 38.7Gy in a single 500ms pulse. The PDD falls to 63% and 48% at 5mm and 10mm depths in solid water. Output was linear with tube current and exposure time (R2>0.99), with minimal ramp up times (0.13ms).
Conclusion: The rotating anode x-ray tube is a viable FLASH radiation source with dosimetric characteristics appropriate for radiobiology research in small animals. In contrast with more advanced accelerator-based FLASH systems, high absolute doses are achievable in a single, continuous pulse. FLASH normal tissue sparing effects have been produced in an in-vivo skin model with this system and are being further explored in a range of treatment sites and tumor models.
Funding Support, Disclosures, and Conflict of Interest: This work was funded by the ASTRO-AAPM Physics Resident/Post-Doctoral Fellow Seed Grant and NIH/NCI 1R01CA262097-01.