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The role of stereotactic body radiotherapy (SBRT) is increasingly attractive for the treatment of spinal oligometastases, with a constantly growing availability of literature experiences. In the present study, we report the results of a multicenter retrospective series of patients who received SBRT for spine oligometastases on behalf of Italian Association of Radiotherapy and Clinical Oncology (AIRO).

The study involved 6 national centers, aiming to evaluate the efficacy of SBRT in terms of local control (LC) and identify predictive factors for clinical outcomes. Survival endpoints were analyzed. Toxicity was assessed according to CTCAE v5.0

From March 2018 to July 2022, 183 lesions in 177 patients with median age 66.5 years (range, 43-89) were analyzed. The most frequent primary histology were prostate cancer in 57%, breast in 26%, lung cancer in 9.6%; oligometastases were oligorecurrent (59%), oligoprogressive (30%) or oligopersistent (11%). In the majority of patients, SBRT was delivered to a single spine metastasis (82%), 2 in 10%, and 3 lesions in 8%, with thoracic spine being the most frequent site of treatment (61.7%), followed by lumbar (33.3%) and cervical (5%). SBRT was mainly delivered with VMAT technique (92%) and HT in 8% for a median total dose of 21Gy (14-35Gy) in 3 fractions (1-5fx) and median BED10=119 Gy (57.7-152Gy). For the entire population, 1-, 2- and 3-years LC rates were 90.3% and 84.3%, respectively. At univariate analysis (UA), prostate histology, oligorecurrent disease and the synergistic use of PET- and MRI-imaging for target volume delineation were found as predictive factors for LC (p=0.002, p=0.09 and p=0.0016), at multivariate analysis (MA), only prostate histology kept significance (p=0.006). Global distant progression-free survival (DPFS) rates were 33.1%, 18.5% and 12.4% at 1-, 2- and 3-years, with prostate histology (p=0.023), oligorecurrent disease (p=0.04) and BED10>100Gy (p=0.04) found as predictive at UA. A further oligometastatic progression was observed in 33 patients (18.6%) treated with a second course of SBRT, reporting at UA slightly improved polymetastatic disease-free (PMS) and overall survival (OS) rates (p=0.07 and p=0.01). PMS rates were 57.8%, 43.4% and 32.4%, with oligorecurrent disease (p=0.001) and concurrent systemic therapy (p=0.0017) being significant for better rates at UA. Only concurrent therapy kept significance at MA (p=0.009). OS rates were 91.8%, 79.6% and 65.9%, with prostate and non-cervical metastases related to better OS at MA. Pain-flare after SBRT was recorded in 3.3%, 5 patients underwent surgical decompression after SBRT, no G≥3 adverse events.

In our experience spine SBRT collected very promising results in terms of safety and efficacy. Prostate histology and oligorecurrent disease resulted as predictive factors for improved clinical outcomes.