Yes, it can be done in certain cases, and is being done more often these days. Like Bart, we probably had more recurrences, more radiation than most here...I had 7 recurrences, 5 neck dissections same side, 5 different radiation treatments, over 192Gy, with three different types, IMRT, HD-IORT and Proton Therapy, and three chemo treatments with 5 different chemo's.

There is really no legal limit to the amount of radiation that can be given, morally or ethically, yes. Although there are limits on the amount of radiation exposure to workers. As mentioned, other factors come to play if radiation can or cannot be done again, and also depends on the time between radiation, the toxicity level to the structure or nearby structures, if part of an area was radiated as opposed to the whole area, the fractions, type of radiation, etc. Somewhere I read the lifetime BID is 137Gy, but haven't been able to re-confirm this or find out what BID means. Radiation is very complex, that's why it takes 2-3 weeks to come up with a radiation plan.

They removed my carotid artery last October, due to cancer involvement, and so I can get more radiation, 10Gy HD-IORT during surgery, which is really 3 times that amount in IMRT, and then 50Gy Proton therapy. To kill HNSCCC the amount usually has to be above 50Gy, really more, otherwise it won't work.

Reirridation tends to be more specific, so they may be able to squeeze in more. I just finished Proton Therapy, and seen patients in thier 80's. Chemo or targeted therapy can be given again, depending on other physical conditions, blood work, kidey, liver function, but they tend to change them since you can become resistant to the ones given, plus if it is a recurrence, apparently didn't work well.

I hope this helps, and good luck.