Purpose: To commission a proton, double-scattering FLASH beamline with maximized efficiency, field size, and to test an SOBP treatment configuration enabling higher-LET FLASH radiotherapy in mice. Our purpose is also to provide a configuration guide for future FLASH proton DS beamlines.
Methods: Beam spot size and spread were measured with film and implemented into TOPAS (TOol for PArticle Simulation). Using TOPAS, Monte Carlo simulations were optimized to verify the ideal positioning, dimensions, and material type of scattering foils, secondary scatterers, ridge filters, range compensators, and apertures. Our in-house experimental FLASH beamline is used to verify these simulations. A ridge filter printed with three discrete heights was used to create a spread-out Bragg peak (SOBP) and was experimentally-verified. Our setup was used to irradiate in vivo mouse brain: n=6 with FLASH treatments and n=10 using conventional treatments.
Results: The configuration and throw which produced the largest field size of acceptable flatness, without drastically compromising dose rate was determined to be an oval field of up to 2 cm x 1.5 cm, roughly 25% larger than the previous configuration. The shoot-through dose rate was measured to be greater than 100 Gy/s. SOBP testing yielded three distinct but connected spikes in dose with flatness under 5%. Reducing the width of the scattering foil by a factor of two was found to increase efficiency by 48%. Mouse cognition testing is underway and currently being evaluated at a collaborating university facility.
Conclusion: We have experimentally established FLASH dose rates of over 100 Gy/s at our double-scattering beamline, increased the efficiency and field size, and enable SOBP treatments by incorporating three different ridge filters. We anticipate the maintenance of FLASH dose rates for SOBP irradiations with larger field sizes, more mice, and future patient treatments.
Funding Support, Disclosures, and Conflict of Interest: Funding Support by the NIH Grant: and by Massachusetts General Hospital Radiation Oncology. No conflicts of interest to disclose.
Not Applicable / None Entered.