Hi, emom ~
I'm not a doctor nor do I claim to be omniscient in matters involving acoustic neuroma surgery and radiation treatment. However, I do know, from my own experience and reading the experiences of other AN patients on these forums over the past 4¾ years, that when the surgeon chooses to leave a small bit of tumor behind, usually for the purpose of protecting the nerve and avoiding facial paralysis, they either observe the remaining AN for possible re-growth with annual MRI scans and/or go straight to radiation treatment following the surgery to head off any possible re-growth.
This was my experience. My neurosurgeon 'de-bulked' my large (4.5 cm) AN down to approximately 2.5 cm, then, (90 days later) I underwent 26 FSR 'sessions' to destroy the remaining tumor's DNA and, in effect, kill it. MY AN symptoms disappeared within 24 hours of the (retro) surgery and I enjoyed a rapid and complete recovery. The FSR sessions were uneventful (I'm not claustrophobic) and successful. My last MRI showed necrosis (cell death) on the tumor and the beginnings of shrinkage. I had to skip 2 years of MRI scans due to financial reasons but hope to be able to have an MRI in 2011. However, I feel great, not a hint of any AN symptoms, and my very (medically) conservative neurosurgeon hasn't requested that I have another MRI so I'm not overly concerned.
So, to answer your question, yes, post-surgical radiation is common on ANs not fully removed but it is not necessarily 'the norm'. Some doctors don't want to take the chance the remaining tumor cells will re-grow so they have the patient undergo radiation. Some simply observe the remaining AN via the annual MRI scans and only recommend radiation if and when growth is clearly noted. In my case, the radiation was part of the overall plan to rid me of the AN and do everything possible to avoid facial immobility, later. It worked.
In your case, with only 1 mm of tumor remaining, I doubt your doctor will recommend radiation. However, even if he does, ultimately, the decision to undergo radiation to kill the tiny bit of tumor that remains is yours, alone. If the very thought of radiation is depressing to you - and you feel symptom-free and not concerned with re-growth - then radiation does not necessarily have to be in your immediate future.
Jim