Stereotactic Body Radiotherapy for Spinal Oligometastases With or Without Simultaneous Integrated Boost: Results From a Monocentric Retrospective Analysis

Aims: Radiotherapy has a known role in the treatment of symptomatic spinal bone metastases, but there is a relative paucity of data for ablative treatments. The aim of our study is to evaluate the efficacy and toxicity of stereotactic body radiotherapy (SBRT) in treating spinal oligometastases. Methods: A series of spinal oligometastatic patients was treated between 2018 and 2023. The clinical target volume was defined according to Cox contouring guidelines. When feasible, a simultaneous integrated boost (SIB) was administered to the site of the macroscopic disease. The primary end-point was local progression-free survival (LPFS). Secondary objectives were toxicity, distant progression-free survival (DPFS), and overall survival (OS). The following covariates were evaluated: SIB, biologically effective dose, histology, number of total metastases (including both spinal and extra-spinal), and concurrent systemic therapy. Results: One hundred and fifty-two spinal oligometastases in 120 patients were treated. Median follow-up was 22 months (range 6–72, with an interquartile range (IQR) of 21 months). Median dose was 24 Gy (range 21–30) delivered in 3 (3–5) fractions. The most common fractionation was 24 Gy in 3 fractions (49 metastases, 32.2%) SIB was administered in 33 metastases (21.7%). One-, and 2-year LPFS rates were 92.1% and 90%, respectively. Moreover, SIB resulted in a significantly improved 2-year LPFS (P = 0.037). Fourteen (9.2%) metastases locally relapsed. One- and 2-years OS were 94.8% and 90%, respectively. One- and 2-years DPFS were 47.8% and 30.8%, respectively, with a median DPFS of 11 months. Oligometastatic prostate cancer patients showed better polymetastases-free survival (PMFS) (P = 0.03) and DPFS (P = 0.008) than other histologies. Conclusions: Spinal SBRT is effective in treating spinal oligometastases. Dose boost could be safely administered to significantly improve LPFS. Prostate cancer patients showed better outcomes.