Proton Radio (5 years out and patch of hair still not back)

Hair follicles are sensitive to radiation (more than skin). Depending on the location of the tumor, and dose of radiation, I think this would be expected. Have you considered any of the hair transplant options? My guess is that minoxidil, which stimulates the existing follicles, might not work, but getting some from elsewhere, and putting them in that spot could really help without needing a large procedure. On the bright side, proton is not usually used except for high risk situations, so 5 years seems like a win!