The Study: It’s about that time of year again. Time for the annual physics and radiation biology board exam for radiation oncology residents. So we thought we’d help you brush up on FLASH-RT, which is basically what it sounds like. Radiation therapy delivered in a FLASH. The typical linear accelerators, even the ones with fancy names, spit out doses of a few Gray per minute. A FLASH linac, on the other hand, can spit out over 100 Gy per second. Meow, the reason this is important is that several groups have observed substantial reductions in normal tissue toxicity with sustained tumor kill at these unprecedented dose rates. This study had two parts. In the first, pig skin was irradiated to escalated doses using conventional and FLASH dose rate electrons. Fibronecrosis was observed at 28 Gy with conventional dose rates, while only depilation (typically seen at much lower doses) was observed even up to 34 Gy with FLASH-RT. Part two was a phase 1 dose escalation trial of FLASH-RT for cats with nasal squamous cell carcinoma. Six cats received from 25 Gy up to 41 Gy in a single fraction. Increasing acute toxicity was observed with increasing doses, mostly desquamation or stomatitis, all of which resolved. All cats experienced a complete response with only one having recurrent disease. There are obviously some challenges when you think about using more conformal targets, but don’t be surprised to see FLASH-RT eventually making its way to cutaneous human malignancy treatments near you.
Bottom Line: FLASH-RT delivered at >100 Gy/s appears safe and effective in cats and could enhance the differential effect of radiation on tumor and normal tissue. And we may have a new neat way to make pork rinds. | Vozenin, Clin Cancer Res 2018