Sorry to hear about the latest development. I suspect the oncologists who said you would not have a reaction were basing that on the fact that AN radiation is very localized, so that only the tumor gets a high exposure. I don't know what sort of systemic disease you may have, and wouldn't know much about it if you told me, but I do think that radiation of a small area like an AN can still trigger some kind of reaction. Inflammation around the AN could cause strange effects elsewhere, for instance.
I suspect that the best you can do is consult with the dermatologist, and treat it however possible. I hope it is not a serious problem and that you can get some help with it.