Repeat Stereotactic Body Radiation Therapy for Spinal Metastases: Long-Term Outcomes and Toxicity.

Background and objectives: Although stereotactic body radiation therapy (SBRT) provides durable local tumor control, management after cases of local failure (LF) continues to remain unclear. This study is one of the largest to report outcomes after a repeat course of spine SBRT after initial SBRT LF.

Methods: A prospectively maintained single-institution database of patients treated with SBRT was analyzed. Inclusion criteria consisted of patients with spinal metastases who underwent a repeat course of SBRT for same vertebral-level LF after initial SBRT. The median dose for repeat SBRT was 16 Gy (range: 12-30) in 1-3 fractions.

Results: A total of 55 patients with 67 metastases met inclusion criteria. Of these, 45 metastases (67%) were irradiated with conventional external beam radiation therapy (cEBRT) before the initial SBRT. The median interval between initial and repeat SBRT was 8 months (range: 2-125). Rates of 6-month, 1-year, and 2-year local control were 96%, 85%, and 77%, respectively. On univariable analysis, only previous cEBRT (P = .014, hazard ratio [HR]: 0.13, 95% CI: 0.02-0.66) was associated with superior local control. Rates of 6-month, 1-year, and 2-year overall survival (OS) were 69%, 53%, and 35%, respectively. Univariable analysis identified age ≤65 years (P = .036, HR: 1.74, 95% CI: 1.04-2.93) and Karnofsky Performance Score >70 (P = .038, HR: 0.57, 95% CI: 0.33-0.97) as associated with superior OS. No tested prognostic factors remained associated with OS on multivariable analysis. Clinical improvement or stability of pain was observed after 95%, 82%, and 75% of treatments at 3, 6, and 12 months, respectively. Accounting for the competing risk of death, the 6-month, 1-year, and 2-year vertebral compression fracture cumulative incidence rates were 6%, 20%, and 25%, respectively. No radiation neuropathy or myelopathy was observed in the follow-up period.

Conclusion: Repeat SBRT is a safe and effective salvage therapy for patients with recurrent spinal metastases after initial same vertebral-level SBRT LF, even in heavily pretreated patients previously irradiated with cEBRT.