For large AVMs that cannot meet the V12 dose constraint, how low are you willing to go in terms of single fraction dosing?

We usually use a “volume staging” approach by treating part of the AVM to 18-20 Gy in one fraction (meeting the V12 dose constraint), and return to treat the remaining nidus about 2 years later. Generally, most or all of the treated nidus has occluded by then. There will, of course, be some dose overlap, but the 2-year interval has made the approach safe in the patients we treated.

I would not go much below 18 Gy. The dose-response really falls off sharply after that for a single fraction, so the various forms of staging are likely equivalent at that point. I have reluctantly pushed V12 up to 12.5 cc in some select situations, but generally stick to 10 cc as my threshold to start to consider some form of staging. I'd consider:

"Volume staging" if the nidus clearly has supply from multiple feeders (I don't like volume-staging otherwise b/c I worry that the flow dynamics may...

Can this staging be done at a shorter interval (i.e., at 4-6 months instead of waiting 2 years)?