UPDATE
Sounds very positive. Remember this is a benign lesion so way less radiation is required. It is tolerated very well and will be daily M-F for 6 weeks. MRI and lazer assisted. Small bits nuked every day.
It is NOT going to debulk it in any way, just make the cells no longer multiply. Not really the same as for cancer.
Sounds like the worst side effect may be - but very slim chances as he puts it - a slight cognitive issue, minor lapses in memory. But this is unlikely.
It will NOT cause cancer it is relatively low dose radiation it just isn't a thing with this. Fatigue will follow treatments.
So it seems like a very positive thing, be nice to stop this from slowly growing.