Top Line: SC.24 provided phase 3 evidence that ablative radiation of 24Gy/2 for painful spine mets doubles complete pain response at 6 months without an appreciable increase in side effects when compared to conventional treatment of 20 Gy/5.
The Study: That’s all well and good, but here is a secondary analysis that may finally win over your next friendly Evicore representative. The question, of course, is retreatment rates. Of 229 patients enrolled on SC.24, 137 (60%) were treated—66 with ablative and 71 with conventional radiation—at the authors’ institution in Toronto and thus had available post-trial imaging and subsequent treatment records. The primary endpoint of local failure (“new or progressive epidural space tumor, gross unequivocal increase in volume or linear dimension, or neurologic deterioration”) after ablative versus conventional treatment, respectively, occurred in 3% versus 11% at 6 months, 6% versus 28% at 12 months, and 15% versus 36% at 24 months. Independent predictors of local failure on multivariate analysis were epidural and/or paraspinal extension (HR 2.07) and, you guessed it, conventional treatment (HR 3.48). And here’s the key point: reirradiation rates at one year were 2% after ablative radiation versus 16% after conventional radiation. Overall rates of vertebral compression fracture were 8% at 12 months and 11% at 24 months. And while there were more fractures attributed to radiation after ablative treatment, there were more fractures attributed to tumor growth after conventional treatment leading to similar fracture rates overall. This is important because it supports the hypothesis that delivering ablative treatment over two versus one fraction(s) can, indeed, halve the risk of fracture.
TBL: 24Gy in 2 fractions for painful spine mets slashes the rate of retreatment without an appreciable increase in fracture risk at 2 years when compared to conventional treatment of 20 Gy/5. | Zeng, Int J Radiat Oncol Biol Phys 2022