2151 - Clinical Outcomes and Dose-Response after Repeat Spine Stereotactic Body Radiation Therapy for Local Failure

03:00pm - 04:00pm ET

Poster Hall - Exhibit Hall A

Screen: 15

POSTER

Presenter(s)

Ian Messing, MD - The Hospital of the University of Pennsylvania, Philadelphia, PA

I. Messing¹, S. Ramesh¹, K. Park², J. Golubovsky², A. B. Adelizzi¹, J. Baron¹, M. Berger¹, M. D. Riina¹, B. Koger¹, V. Dolney¹, R. M. Scheuermann¹, A. Hassankhani³, C. Freeman³, J. M. Schuster², J. H. Shin², N. R. Malhotra², G. W. Peters¹, and A. A. Butala¹; ¹Department of Radiation Oncology, University of Pennsylvania, Philadelphia, PA, ²Department of Neurosurgery, University of Pennsylvania, Philadelphia, PA, ³Department of Radiology, University of Pennsylvania, Philadelphia, PA

Purpose/Objective(s):

Repeat stereotactic body radiation therapy (SBRT2) is increasingly used for spinal metastases progressing after prior SBRT (SBRT1), yet outcomes, dose–response relationships, and patient subgroups most likely to benefit remain poorly defined. We hypothesized that minimum delivered target dose is a key determinant of local control (LC) after SBRT2 and that selected patients with limited metastatic burden achieve favorable outcomes.

Materials/Methods:

Patients undergoing SBRT2 for in-field failure or adjacent-level progression after SBRT1 between 2018–2025 were retrospectively analyzed. The primary endpoint was LC. Secondary endpoints included overall survival (OS), pain response, toxicity, and predictors of outcome. Dose heterogeneity was assessed using minimum dose to 0.03 cc (Dmin), expressed as EQD210. LC was analyzed using cumulative incidence and Fine–Gray regression. OS was estimated using Kaplan–Meier and Cox regression.

Results:

Forty-nine patients underwent SBRT2 to 115 vertebral segments. Median follow-up was 10.4 months. Median OS was 17.6 months, with 6- and 12-month OS of 76% and 57%. Disease extent strongly influenced survival. Patients with oligometastatic disease demonstrated excellent outcomes, with 6- and 12-month OS of 94% and 88% and median OS of 31.6 months, compared with 64% and 36% and median OS of 7.4 months among patients with extensive disease (P<.001). ECOG performance status further stratified survival (P=.005).

With death as a competing risk, cumulative incidence of local failure was 15% at 6 months and 25% at 12 months. Target dose significantly influenced LC. Patients treated to Dmin =28 Gy EQD210 had lower 12-month local failure compared with <28 Gy (6% vs 36%; Gray’s P=.034). On univariable competing-risk regression, increasing Dmin (SHR 0.27; P=.029) and higher CTV D90 EQD210 (SHR 0.94 per Gy; P=.021) were associated with reduced failure risk. Epidural disease accounted for most local failures. Oligometastatic patients demonstrated low early failure, with 6- and 12-month local failure of 6% and 12%.

Among patients with baseline pain, complete or partial pain response at 3 months occurred in 55%, with durable response in 46%. No radiation-induced myelopathy occurred, and crude vertebral compression fracture rate was 12%. No grade =3 radiation-related toxicities were observed.

Conclusion:

Repeat spine SBRT provides meaningful LC and pain relief with low toxicity in selected patients. LC after SBRT2 is dose dependent, with minimum delivered target dose emerging as a key determinant of outcome, while survival is driven primarily by disease extent and performance status. Outcomes are particularly favorable in oligometastatic patients, in whom survival and early LC approach those reported for de novo spine SBRT. These findings support multidisciplinary selection and careful treatment planning when considering salvage spine SBRT.