Gross Tumor Volume as a Predictor of Local Control After Stereotactic Body Radiotherapy for Bone Oligometastases: A Retrospective Analysis.

Abstract

Bone oligometastases are increasingly recognized as a clinical entity that may benefit from local therapies. Stereotactic body radiotherapy (SBRT) enables the delivery of high-dose, precise irradiation and has shown promising results in improving local control (LC) and survival. However, prognostic factors influencing LC after SBRT in patients with bone oligometastases treated with curative, metastasis-directed intent remain unclear. We retrospectively analyzed 58 patients with 68 bone oligometastatic lesions treated with SBRT between March 2021 and December 2023. Radiotherapy protocols were determined according to lesion site, and follow-up imaging was performed every three months. Overall survival (OS) was evaluated using the Kaplan-Meier method, and local control (LC) was assessed using a competing risk model. Prognostic factors for LC were investigated using univariate and exploratory multivariable analyses, with gross tumor volume (GTV) cutoffs determined by receiver operating characteristic analysis using local recurrence as the endpoint. The median follow-up duration was 25 months. The 1- and 2-year OS rates were 95% and 80%, respectively. The 1- and 2-year LC rates were 86.1% and 80.3%, respectively. On exploratory multivariable analysis, GTV ≥ 12 cc was identified as an independent predictor of local recurrence (adjusted HR = 8.77, 95% CI 1.10-70.2, p = 0.041). Lesions with GTV ≥ 12 cc had significantly lower LC rates than those with GTV < 12 cc (Gray's test, p = 0.013). No grade ≥3 treatment-related adverse events were observed. SBRT for bone oligometastases provides excellent LC and survival with minimal toxicity. Larger tumor volume, as assessed by GTV, was associated with a higher risk of local recurrence in this cohort. Further studies are warranted to validate these findings and to explore volume-adapted treatment strategies.