The only thing I've heard of to help mitigate this is stretching the muscles that were radiated. I'm coming up on six months post-treatment and I can feel the muscles in my neck and jaw trying to tighten up. I stretch these muscles several times a day.

To stretch my jaw: I simply open my mouth as wide as it will and then stick my tongue as far as it will go. Of course, this looks silly, but I don't care.

To stretch my neck: While keeping my mouth closed I look up as far as I can. Then while still looking up, I look to the left and to the right. This is usually painful, but I really don't want to lose any more mobility in my neck.

Hope this helps.

-Brett