Usually it has to be above 50Gy, if not more, to kill SCC. I had 50Gy IMRT, and 50Gy Proton for two recurrences, but I also had HD-IORT, 12Gy and 10Gy, as a boost, which is equivalent to 3 times that in IMRT, and a pec flap, so was able to receive even more radiation, although the radiated field was smaller, and it also depends on the maximum dose toxicity level of the structure or nearby structures involved, and prior radiation.