Room: AAPM ePoster Library
Purpose: Ultra-high dose rate (“flash”) radiation therapy has been of interest recently for the potential increase in therapeutic index by decreasing damage to normal tissue while maintaining tumor treatment response. While electrons have been studied previously, protons have the capability to improve spatial dose delivery due to the nature of proton dose deposition. In order to utilize these spatial advantages, the use of the Bragg peak was investigated for flash studies.
Methods: A fixed horizontal research beam was used for this study. The proton beam can deliver 70-230 MeV protons to a photon small animal radiation research platform (SARRP) on-rails with imaging capabilities for target alignment. Control systems have been developed to deliver the beam with flash dose rates (>75Gy/s) as well as standard dose rates (0.5Gy/s) with the same treatment geometry. A ridge filter was used to create a spread out Bragg peak (SOBP) usable for irradiating the whole abdomen of mice. Depth-dose characteristics of the SOBP were measured using a multi-layer ionization chamber and absolute dose measurements were performed with an Advanced Markus chamber according to IAEA TRS-398 code of practice. Beam profiles were measured with EBT3 film and Lynx scintillator detector.
Results: Recombination was measured and found to be negligible for both flash and standard dose rates at the entrance region and the SOBP. The resulting SOBP had a width of 2.8cm with a lateral dimension of 2.3cm at the D90 line. The SOBP was verified with both the ion chamber measurements and film. Bragg peak properties were measured for conventional and flash dose rates using the same irradiation geometry. Flash dose rates as high as 160Gy/s were achieved at the entrance and mid-SOBP.
Conclusion: A ridge filter was developed to create a usable SOBP for irradiation of mouse whole abdomen at flash and conventional dose rates.
Funding Support, Disclosures, and Conflict of Interest: L.D. reports personal fees from Varian Medical Systems Speakers Bureau and other from Varian Medical Systems, outside the submitted work. J.M. reports other from Varian Medical Systems Advisory Board, other from Ion Beam Associates Advisory Board, other from Provision Advisory Board, outside the submitted work.