Published in the Red Journal by the UPenn group, this paper reported the effect of FLASH proton versus standard dose rate PRT on tumors and normal tissues in mice. Dose rates of 78 ± 9 Gy per second and 0.9 ± 0.08 Gy per second for the FLASH and standard PRT were delivered. Whole abdominal FLASH PRT at 15 Gy significantly reduced the loss of proliferating cells in intestinal crypts compared with standard PRT.

Studies with local intestinal irradiation at 18 Gy revealed a reduction to near baseline levels of intestinal fibrosis for FLASH-PRT compared with standard PRT. Despite this difference, FLASH-PRT did not demonstrate tumor radioprotection after 12 or 18 Gy irradiation. The study concluded that FLASH-PRT decreases acute cell loss and late fibrosis after whole-abdomen and focal intestinal RT, whereas tumor growth inhibition is preserved between the 2 modalities.