The trial I've been waiting years for is finally out (Wijesooriya et al, IJROBP). First randomized evidence that proactively sparing the blood- and immune-rich organs during lung SBRT - thoracic spine, lymph node stations, heart, great vessels - reduces radiation-induced lymphocyte kill. And it does it inside standard RTOG 0813/0915, so this isn't a research-only technique. The numbers are hard to ignore. ALC preservation improved 13.4% overall and 29.5% for central tumors. Grade 3 lymphopenia went from 15.4% in the standard arm to zero in the optimized arm, with no toxicity penalty - if anything, fewer high-grade events. In treatment-naïve patients, exploratory 2-year OS was 94% vs 69%. Underpowered and hypothesis-generating, but the direction is striking. Here's where I have to update my own priors. I've argued lung V5 was the last frontier for RIL, and I've framed immune sparing as a trade-off, step on the balloon, dose has to go somewhere. But lung V5 and V10 were essentially identical between arms. The dose taken off the spine and vessels wasn't relocated into lung; it was largely eliminated, and whole-body integral dose actually dropped. The balloon had somewhere better to go than I assumed. One caveat I can't resolve from this report: the dosimetry is pooled, and the cohort is mostly peripheral tumors. For central tumors, where the spared mediastinum sits right against the target, I'd still expect lung V5/V10 to rise. We just can't see it broken out here. And the metric that predicted survival wasn't EDIC. It was lymph node V5. Organ-specific beats the lumped immune-dose number, and that reframes how we should be optimizing these plans. #OncTwitter #LCSM