Lucky ~
I'm not a doctor but I can tell you with certainty that your AN is small (mine was 4.5 cm). That being the case, as others have noted, you should be able to observe the AN to see if it is growing or stable. Another MRI scan in three to six months should suffice.
You should never forget that you are in charge at this point. Dr. Duma, who has an excellent resume, can offer his medical advice but ultimately, you call the shots, as it were. Do not be frightened into doing anything rash or unnecessary.
As for the efficacy of Gamma Knife radiosurgery, it has been in use since 1988 and thousands of AN patients have benefited from this procedure. Because I'm not one of them (I had FSR) I'll leave to those with first-hand GK experience to comment on the experience. However, I believe that it is accurate to state that the chances of an irradiated acoustic neuroma metastasizing is infinitesimal and not something you should be concerned about. However, many doctors steer younger (under 65) AN patients away from radiation procedures (GK, CK, FSR) due to concerns about the patient accumulating too much radiation for their body to safely absorb. That idea is losing credibility but old ways die hard and many doctors still hold that view. Apparently Dr, Duma isn't one of those - or you're 'old enough' that he isn't overly concerned about your radiation intake. In any case, please think about this and do not rush into any procedure. We've had members - frightened by their doctor's grave concerns - that did just that and regretted it, later. Radiation treatments may be 'non-invasive' (no cutting) but they are not a panacea. As with surgery, GK carries it's own risks. I'm sure GK patients will soon add to this thread with more information based on their experience. I suggest that you consider their words.
Jim