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Top Line: The SC.24 trial reported initial outcomes at ASTRO 2020 consistent with a significant improvement in pain response with ablative (24Gy/2) versus conventional (20Gy/5) palliative spine radiation.
The Study: We now have the full manuscript to peruse, and there’s a lot to unpack. The real question to be answered is how to reconcile these findings with conflicting ones, and the answer likely lies in key variations in inclusion criteria, prescription techniques, and, perhaps most importantly, primary endpoint. So let’s break this one down. Key inclusion was ≤3 consecutive vertebral bodies in treatment volume, SINS <12—a crucial common sense criterion (not used in the notorious 0631) since radiation won’t fix instability, and, importantly, no neurologic deficits from compression of cord or cauda equina. The big win came in the form of a primary endpoint of complete response for pain at 3 months: 40/114 (35%) versus 16/115 (14%) of 115 after ablative and conventional radiation, respectively. While pain responses occur on a spectrum of degrees and time points, complete pain response is arguably the most reliable and least subjective palliative endpoint. On that note, the rate of any pain response at 3 months was 56% versus 39%, respectively, and complete pain response was stable at 6 months with rates of 32% versus 16%. Staying on that note, and specifically with Evicore in mind, since the endpoint was purely palliative in nature, the study population was not limited to oligomets or specific histologies. In terms of toxicity, “a similar incidence of vertebral compression fractures between the two groups and the significant improvement in the total SINS from baseline at 3 months support the biomechanical safety of [the ablative] regimen.” But with a reported occurrence of only n=1 in each arm, we’d be remiss not to speculate that those curves will likely separate with time in favor of conventional treatment (though the authors did choose 24Gy/2 versus 24Gy/1 precisely to limit fracture risk). We’ll end with an intriguing finding. The only significant difference in quality of life change after treatment was financial burden, in favor of ablative treatment, presumably due to the decreased burden of 2 versus 5 days of treatment.
TBL: Ablative spine radiation, specifically with 24Gy/2, more than doubles the rate of complete pain response when compared to conventional radiation techniques with no increased toxicity in the first 6 months. | Sahgal, Lancet Oncol 2021