Hi koch and welcome.
Not knowing the specifics of your AN situation (ie; size of growth, exact location of growth -- in the IAC or sticking out, pressing or not against brainstem, etc), what I can tell you is this..... as one that had radiosurgery over 4-1/2 yrs ago in Boston.
I did an extensive amt of research into radio for my particular AN situation. Choosing a radio center (regardless if GK or CK or Proton or Trilogy, etc) should be done with care. Being able to know the # of AN's treated is important... IMO, I wanted to make sure that whomever "zapped" my head knew what they were doing. I also inquired about "patient referrals" for the radio centers to see if they had "treated" patients willing to talk to me about the particular dealings with the radio-center. I was truly lucky to find this forum (over 5 yrs ago) to help gain insight into the processes and happen to have those on these forums that knew of particular teams and how they did.
I do know, from a New England standpoint, that Tufts does have a great GK center. There is a user on this site named "helga" that was treated at Tufts and would be a good resource. I also know that Dr. Georg Noren in Providence is a leader in GK, regardless of where in the USA. He's been on the forefront of experimentation with GK (ie; fractionating vs. single dose, etc) and I know of folks that were treated by him that were happy with their results. I know, first hand, of other radio treatments in Boston such as Cyberknife and Proton that many of us have had and are pleased.
In fairness, I also know of some that did not have the results they hoped. As with any AN treatment option, there are risks, success rates, after affects, etc to take into consideration.
To help determine what will be best for you and your situation (as we tout here, it is a highly personal decision and should be done based on your situation, from the AN itself to insurance to travel distances, etc), see if any of the centers you are researching will give you direct patient references. I can speak on behalf of personal experience of Beth Israel and Brigham/Woman's as I have 2 teams in place for my AN. I know of many here on the forums that can speak to Proton treatment at Mass Gen Hosp/Mass Eye and Ear..... and as noted, I know of Helga for Tufts and one or 2 for Dr. Noren.
Suggestion is to do a "search" option on these forum home page for the particular centers (ie: type "Tufts" in the search box or "Beth Israel", etc)... you will see past discussions for many of these centers based in New England. It should also help give insight.
I hope this helps. Again, welcome.