Two much, or not enough?

Top Line: SC.24 showed that spine SBRT (24 Gy in 2 fractions) improves pain control and local control compared to conventional palliative radiation.

The Study: Is further dose escalation beneficial without increasing fracture risk? This retrospective analysis from Sunnybrook compared outcomes from spine SBRT using a dose of 28 Gy in 2 fractions compared to the standard 24 Gy in 2 fractions. Among 482 patients with 947 spine metastases, 68.2% received 28 Gy and 31.8% received 24 Gy. Dose escalation was performed while seeking to meet the same spinal cord dose constraint. In SC.24, the spinal cord PRV (cord + 1.5mm) or thecal sac max dose constraint was 17 Gy. Across this study period, the maximum cord PRV/thecal sac dose was limited to 14.5-19.3 Gy for de novo treatment and 11.0-16.1 Gy for reirradiation. Patients receiving 28 Gy were more likely to be receiving post-op treatment (18.6% v 10.4%), have SINS stable disease (64.1% v 55.4%), and have no paraspinal extension (83.7% v 65.6%). The rate of local failure was significantly lower after 28 Gy (11.6% v 21.7%), and median time to LF was 13 months compared to 9.9 months with 24 Gy. Factors associated with an increased risk of LF on multivariable analysis were receipt of 24 v 28 Gy, paraspinal disease extension, and epidural extension. There were no cases of myelopathy, and there were a few (<5%) grade 1-2 plexopathy events. There was no increase in the rate of vertebral compression fracture (VCF) with dose escalation (12.3% v 11.6%), which remained well below the risk reported with dose-escalated single fraction regimens. Factors associated with VCF risk were increasing PTV D90% and pre-existing structural compromise of the spine.

TBL: Dose escalation of spine SBRT to 28 Gy in 2 fractions appears to improve local control without significantly increasing the risk of toxicity or vertebral compression fracture. | Zeng, Int J Radiat Oncol Biol Phys 2022