Shoot straight.

Headline: Spine radiosurgery (SRS) doesn’t improve pain control over the tried and true 8 Gy x 1.
The Study: What’s that we hear? The cries of woe of disappointed radiosurgeons everywhere. We finally have results of the phase 3 RTOG 0631 that randomized 330 patients with “limited” (read: 1-3 different sites with no more than 2 contiguous levels involved) spine mets to either a sophisticated SRS approach of 16 (55%) to 18 (45%) Gy x 1 with rigorous dose constraints and quality assurance...or a conventional set-up of 8 Gy x 1. Crucially important here is the choice of primary endpoint. The more obvious choices of local tumor control or durability of pain control be damned, the authors opted instead for patient-reported pain control (read: at least a 3 point improvement on a pain scale 0-10) at 3 months. This happened in 40% of patients after spine SRS and...wait for it...58% after conventional treatment. This numerical inferiority of SRS was unexpected, to say the least, though the gap did almost close by 6 months. Predictably, the discussant hypothesized the SRS dose was simply too low. Since we weren’t asked to discuss elsewhere, we’ll discuss here that it might have something to do with the drastically different target volumes between arms—the involved spinal segment alone with SRS versus the entire vertebral body plus one above and below with 8 Gy x 1—keeping in mind, when in comes to bone pain, there are many more local factors at play than simply the presence of active tumor.
TBL: We’re gonna shoot straight here: it just got more difficult to justify upfront spine SRS for most spine mets. Ryu, ASTRO 2019


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