Session Item

To investigate the normal tissue sparing effect of FLASH radiotherapy a research proton beam line was commissioned to deliver ultra-high dose rates for pre-clinical studies. Many groups have been investigating the use of electrons for ultra-high dose rate studies; however, protons provide unique advantages due to their physical properties. A double scattered system was devised with appropriate collimation for use in small animal studies. Absolute dose was measured using a NIST-traceable calibrated Advanced Markus chamber and validated against absolute integral charge measurements using a Faraday cup. Initial studies included mouse whole abdomen irradiation with both FLASH and standard dose rates to compare fibrosis and loss of proliferating cells in intestinal crypts with a shoot-through proton beam of 230 MeV. Later studies included the use of a ridge filter to determine if the FLASH effect was seen in the spread-out Bragg peak (SOBP). Proton FLASH studies show increased normal tissue sparing in in vivo models using both the shoot-through and SOBP techniques as well as equivalent tumor control between the two dose rates. Real-time dose rates were determined using a NaI detector to measure prompt gamma rays. Beam control systems were validated to have accurate control of beam flux on a millisecond time scale. After initial commissioning activities and verification of dosimetry, the research beam line was also utilized for the enrollment of canine patients for a large animal clinical trial.