Hi John,
I have 4+ years with similar conditions, tonsil treatment, IMRT and I see a hygenist 4 times a year, rather than the 2 that insurance pays for. I still floss daily, use a Water Pik and in home flouride treatments. I have had a few filings replaced and some minor repairs. They have started using digital xirays to visualize areas that they cannot see (like plaque buildup between the teeth)and the hygenist does below the gumline cleaning, with ultrasonics as well. Certainly the radiation was very hard on the gums and I have grown much "longer in the tooth" as a result. The roots are far more vulnerable and you have to even more diligent with oral hygiene - and for life at that.