Brendan

When I joined OCF, the majority of posters were told by their radiologists that they could not have radiation twice because of the probability of what your radiologist warned: necrosis and or carotid artery damage. It turns out that you can have radiation multiple times, the key is to avoid as much "cross over" into the former radiation areas. That usually requires a more precise means of radiation delivery than the first way. In my case, the radiologist switched from standard IMRT to CyberKnife (a form of SRT).
It would not hurt to ask your radiologist if there is a version of CyberKnife or SRT available in your area. That way the amount of "cross over" can be limited easier than using IMRT a second time.
Still, the numbers sounded pretty good to me: 95% chance of success - I've never had any oncologist give me more than a 50% chance. Maybe there is not too much crossover
Charm