Michael, I have been thinking about you and want to share my dad's experience (since you are embarking on what he did 3 weeks ago).
He went from eating pizza with us one day to radiation sores in his mouth the next. Since he wasn't expecting the pain to creep up on him like that, he spent the whole week trying to catch up with the severe discomfort. Please, get your pain meds now and the minute you get a hint, start taking them. He is now in the hospital with fever spikes-his labs are NORMAL. From what I've learned, this is usual.