Dad is starting 4th week of IMRT-his mouth one uninterrupted sore-but, his tumor is "significantly" and "profoundly" (MD's words). The cumulative effects of the rad came over night. One day we were eating pizza, the next he was shaking with pain. This is our experience-there is no way to prepare. BUT even NOW, my dad says that this is path to killing the little mother F-er in his throat. Having sharing that, the IMRT is the way to GO!!!
Ensure you are stocked with your pain meds BEFORE it starts. He doesn't have the PEG tube yet but he is down to ONLY LIQUID nourishment.
Best of luck-we are all with you.