The situation is kind of like black hole mergers; the closer the two things get, the "hotter"* the intervening space gets. Can't defy the physics in either situation. You make it be as good as it can is the cop-out answer. The highest dose(s) in the plan should still be the centers of targets... not out in the invisible bridges between (keeping in mind what a "hot spot" truly is). Inverse optimization allowing heterogeneity (ie Dmax's that are up to 50% hotter than the Rx dose, aka Rx'ing up to the ~67% line) plus a single isocenter approach are your friends, if they're not already. Another help is to use beams that are in a plane, or close to a plane, that is perpendicular to a plane that holds the isocenters of the two targets; only applies in two target problems cases really though.How do you guys handle SRS planning with closely adjacent lesions...say separated by a few mm? What kind of hot spot are you willing to accept in normal brain tissue in the "bridge" between the lesions?