Just noticed this thread and thought I might be able to add something useful.
I was diagnosed with an AN tumor too large to radiate (see my signature) so, to avoid possible nerve damage, my neurosurgeon recommended that he 'de-bulk' the tumor (hollow it out, in layman terms) and that I then undergo FSR to kill the remaining portion. I did just that. The surgery was successful - the surgeon was able to remove over 50% of the tumor - and my recovery was uneventful with no post-op complications. 3 months later, I began 26 FSR treatments, which were a bit tedious but also relatively uneventful. I finished those in mid-October of '06. So far, so good. No complications. I just found out (last week, in a follow-up visit with my radiation oncologists successor) that a December '06 MRI indicated that the tumor showed signs of necrosis. I was elated! My radiology oncologist said that tumor shrinkage may take a few years but the highly focused, low-dosed radiation obviously worked well. I have another MRI scheduled for April. Naturally, I hope to see even more signs of necrosis.
No matter how you approach it, I believe that radiation is a very viable form of treatment for AN tumors. Had mine been small enough upon diagnosis, I would have went with radiation (in some form) to deal with it. That wasn't an option but I did the next best thing and I have no regrets.