That's rough. Kyphoplasty seems safer for extravasation because of that space made by the balloon or osteotome, but you can create a cavity without a balloon. Drill a path, come back to the pedicle, then take another route at a slightly different trajectory. You're just trying to keep from injecting into a tight space right away where you're really flooding the vasculature.
Make sure you're anterior before you start injecting
Inject at lower pressures initially with multiple shots in the first 0.5 to 1 mL
Wait for the cement to be a touch more viscous/gummy in your hand before injecting into the body
The final volume is irrelevant to me as it's more a matter of where you inject and whether it's leaking.
The goal should not be to have zero leaks. Reality isn't going to allow for that. The goal needs to be identifying when you're leaking and to minimize symptomatic/dangerous leaks.