There are studies beginning to appear indicating that proactive treatment with Gamma Knife may provide better hearing preservation than Watch and Wait. There also some papers on pubmed showing AN's that are growing outside the IAC like yours are more likely to grow.
Have a read of these links.
http://www.ncbi.nlm.nih.gov/pubmed/21121792http://www.ncbi.nlm.nih.gov/pubmed/22682708http://www.ncbi.nlm.nih.gov/pubmed/22937934One of my Local doctors had a very strong opinion on W&W as the preferred management option.
In the last 6 months he has changed and his patients are now increasingly being proactively treated with Gamma knife to preserve hearing.
www.pubmed.com is a wealth of information, although it can be scientific and full of statistics which need to be interpreted.
There are quite a few papers showing that hearing preservation is strongly related to Cochlear Dose, far more so than fractionation.
Therefore choosing the most accurate equipment and experienced operators is very important to reduce cochlear dose.
As for fractionation there appears to be some very slight advantage in hearing preservation however it comes at a cost, and probably applies more to larger tumours more than smaller ones and has yet to be definitively proven.
There is a thing called the alpha/beta ratio.
Its how tumour and healthy tissues behave after radiation.
With Acoustic Neuromas the alpha/beta ratio is such, that fractionation is not as effective as other tumours in preserving healthy tissue.
There is also diminishing returns with each fraction for preservation of good tissue.
So if fractionation helps..... and that is still debatable with AN's, going beyond 3-5 fractions may provide negligible benefit while exposing the patient to increasing amounts of radiation.
Each fraction means your total exposure to radiation increases. there is also radiation leakage from the equipment and scattering of radiation from your head, the equipment and the room.
This is why radiation oncologists try to reduce treatment times to reduce radiation exposure to the rest of the body.
These doses are significant and do add to your lifetime cancer risk
Single session radiosurgery is typically provided in a single dose of 13Gy while 25 sessions of Radiotherapy is typically 50Gy
Its been nearly 4 years since I was treated with Cyberknife and I still have my hearing and life goes on like normal..
I chose to have radiation done proactively to preserve my hearing, my second choice would have been W&W.
If I was deaf I probably would have chosen W&W until significant growth was detected, then radiosurgery
The amount of radiation you receive is proportional to the volume of your tumour also, another reason to have the tumour treated sooner rather than later.
Please do your own research, the above is my personal opinion, I am not a medical professional.