Trying having him spit right before he lays down and maybe using a lubricating throat spray or drops to suck on. That mask that they snap on, think of it a super hero uniform or being shipped off into space. They played music during my radiation, I started out with light soothing but in the end I wanted loud and hard. It made me feel so much better.
After radiation and chemo, he's going to feel worse before he feels better. The two weeks right after and usually horrible and then slow climb out but not that slow. It's different for everyone.
Make sure he takes good care of his skin.