Abstract
Recent data suggests that "ultra-central" tumors, generally defined as those abutting the proximal airways, are at particularly high risk for severe complications when treated with stereotactic ablative body radiation (SABR). However, this association has not been consistently demonstrated across reports, possibly due to small numbers, varying definitions of "ultra-central", and the lack of prospective data. New evidence suggests that exposure to VEGF-inhibiting agents may potentiate SABR toxicity and may partially explain the disproportionately high incidence of fatal complications in some reports. Efforts are underway to identify dose-volume limits that can predict complications involving central structures such as the proximal airways, heart, esophagus, and great vessels. The optimal dose for ultra-central SABR has not been determined, though there is a trend towards using more highly fractionated regimens. Further research into the safety of SABR for ultra-central tumors is needed, given the lack of other effective local therapy options for this clinical scenario.