Room: AAPM ePoster Library
Purpose: 1) To modify a clinical treatment unit to achieve FLASH dose rates and demonstrate the feasibility of irradiations with FLASH rates, including PBS (pencil beam scanning) conformal irradiations. 2) To define the monitoring and safety requirements for future FLASH experiments with protons.
Methods: A recently de-commissioned treatment PBS gantry has been adapted for experiments in FLASH mode. As it is equipped with a fully automated, discretized and nozzle mounted range shifter, adaption to FLASH type irradiations will allow for detailed studies of this effect in different parts of the Bragg peak curve. We optimized beam optics to transport an un-degraded proton beam from the cyclotron to the isocenter. Dose monitoring for 100 times higher dose rates was studied and suitable solutions were developed. We characterized the beam in air for different beam widths and measured depth-dose curves in water. Safety requirements have been defined and additional supervision systems implemented.
Results: The optimized beam optics transport a 2.5-mm (sigma) beam of 250-MeV protons, with a current of 700 nA and higher, to the isocenter with a transmission efficiency of 85%, providing a dose rate of 3800 ± 100 Gy/s at the sample. Doses of up to 40 Gy have been delivered to water samples of 0.2 mL with an irradiation time of the order of 10 ms. As such, implementation of biological experiments with cell lines and small animals will take place soon.
Conclusion: A previously clinical PBS proton gantry has been successfully modified into a test bench for FLASH irradiations with protons. In addition to shoot-through, it could also allow conformal (Bragg peak) PBS irradiations to be conducted in FLASH mode. As such, we have successfully prepared the gantry for first biological experiments to be conducted in the next months.
Funding Support, Disclosures, and Conflict of Interest: The work was partially funded by the Swiss National Science Foundation (CRSK-2_190663).