KEY POINTS
- This retrospective multidisciplinary spine-program series included 49 patients undergoing repeat SBRT to 115 vertebral segments after either in-field failure or adjacent-level progression following previous spine SBRT.
- Patients were clinically high risk: 61% had extensive metastatic disease, 45% had ECOG ≥2, 43% had radioresistant histology, and 43% underwent decompression or stabilization before the second SBRT course.
- Median first-course treatment was 27 Gy in 3 fractions, while repeat SBRT delivered a median 30 Gy in 5 fractions. The median interval between courses was 14.7 months.
- Local failure after repeat SBRT was 15.0% at 6 months, 24.5% at 12 months and 33.1% at 24 months. Most failures occurred relatively early, with a median time to local failure of 6.2 months.
- Minimum target dose showed a strong dosimetric association with control. Patients receiving Dmin ≥28 Gy EQD2₁₀ had 5.6% local failure at 12 months versus 36.4% with Dmin <28 Gy, and increasing Dmin was associated with a lower risk of local failure.
- Among patients with baseline pain and available three-month assessment, 55% achieved complete or partial pain response, while 46% had a durable response. Oligometastatic patients had much longer median survival than patients with extensive disease: 31.6 versus 7.4 months.
- Toxicity was reassuring for such a heavily pretreated cohort: no radiation-induced myelopathy and no grade ≥3 radiation-attributable toxicity occurred. The crude vertebral compression fracture rate was 12%, and VCF was associated with a higher risk of subsequent local failure.
CLINICAL TAKEAWAY
Repeat spine SBRT after prior SBRT can provide useful salvage control and pain relief in selected patients without an obvious excess of severe neurologic toxicity. The Dmin signal suggests that preserving sufficient minimum target dose may matter, but smaller targets and other favorable characteristics were more common in the higher-dose group, so 28 Gy EQD2₁₀ should not be treated as a validated threshold.