The normal tissue sparing effects of ultra-high dose rate radiation (FLASH) remain poorly understood. At University of Washington, a cyclotron beamline has been modified to produce a 50 MeV proton beam at dose rates between 0.1 to 100 Gy/s for preclinical research. We used C57BL/6 mice for whole lung and whole abdomen radiation with conventional (~ 0.5 Gy/s) and FLASH (42-70 Gy/s) dose rates. Mice were observed for dermatitis and weight loss. Lung and colon tissues were harvested post-radiation (1-hour, 5-days, 1-month, 3-months, 6-months). H&E and immunohistochemistry was performed for: yH2aX, cleaved caspase-3, trichrome, MAC2 and F4/80. More radiation dermatitis was observed in the conventional group. 1-hour post radiation, lower cleaved caspase-3 IHC staining was seen in the FLASH group versus conventional group, while yH2aX staining was similar in both groups. More lung airspace disease (fluid and inflammatory cells) was seen in the conventional group at 6-months. The preliminary results suggest FLASH proton radiation leads to less normal tissue toxicity than conventional dose rate radiation. More studies are ongoing. 

Short bio:
After I received my PhD in Medical Physics from Purdue University in 2012, I joined the Medical Physics Residency program at University of Washington. In 2014, I started to work at Seattle Proton Center as a proton physicist and in 2015, I joined the medical physics faculty group at University of Washington. My research interests are cellular and small animal radiation therapy. My current research focus is the normal tissue sparing effects of FLASH proton radiation.