Bette, Colleen is right on target with "magic mouthwash" it will help, as will club soda. He will need to get some pain meds started, and likely soon. Once the rad side effects start, they tend to advance fairly quickly.

He will start to feel unwell, and it will steadily worsen over the next couple of weeks. There's light at the end of the tunnel though.

Even with a PEG, it's REALLY important that he keep swallowing. He needs to keep up his hydration, and if he stops swallowing for even a short while, it will be a hard skill to regain. Have him drink as much as he can, even with his PEG. If you have ANY questions, please ask away.

I had six weeks of radiation following surgery last year, so I can try and help you as much as possible.
Much luck
Wayne