phx ~
If you're concerned that the AN will somehow increase it's growth rate due to being irradiated, I doubt that is anything to worry about. Basically, as my radiation oncologist radiation explained it, the radiation (GK,CK,FSR) destroys the tumor's DNA, stopping it's growth and eventually killing it, entirely. Sometimes the radiation doesn't quite destroy every tumor cell so the AN re-grows. I haven't heard of a radiated tumor growing faster and I'm skeptical that this would happen.
We want to help but for the most credible answers to questions such as this, I would suggest you pose your concerns to a radiation oncologist, as he would have better knowledge of all the possible ramifications inherent in radiation treatment for an acoustic neuroma, including possible re-growth rates. I'd be interested in his answer to this question.
Jim