The aim of gamma knife treatment for most benign tumours is to arrest the growth of the tumour and halt the progression of related symptoms. The effects of treatment are not seen immediately and generally take place gradually over many months. For this reason it is not normally necessary to have a follow-up scan until 9-12 months post treatment.
The aim of gamma knife treatment for AVMs is to obliterate them. This process of obliteration usually takes place over a period of 2-3 years following treatment. An MRI scan is usually performed 2 years post treatment and repeated every 6 months until the AVM can no longer be seen. At this point an angiogram will be performed as confirmation of effective treatment.
Obliteration can take longer than 3 years and treatment is not considered to have failed unless the AVM, or a part of it, can still be seen 4 years post treatment.