Improved local control following dose-escalated stereotactic ablative radiation therapy (SABR) for metastatic sarcomas: An international multi-institutional experience

Abstract

BackgroundWe aimed to characterize local control (LC) and overall survival (OS) following stereotactic ablative radiation therapy (SABR) for extracranial sarcoma metastases. MethodsA prospectively-maintained institutional registry was queried for patients with metastases from sarcoma primaries managed with SABR. Kaplan-Meier analysis was utilized for univariate analyses to assess potential prognostic factors regarding LC and OS. A Cox proportional hazards multivariate (MVA) model was employed to further assess initially identified independent variables. ResultsA total of 94 patients with 118 lesions with LC information were identified. Common metastatic sites treated were lung (77), non-spinal bone (15), and spine (10). The median biologically effective dose (BED4) was 175 Gy4 (range56.3 Gy4–360 Gy4) with a median dose/fractionation schedule of 50 Gy/5 fractions. One- and 2-year OS rates were 81.3 % (95 % CI: 71.2–88.1 %6) and 50.5 % (95 % CI: 38.6–61.3 %, respectively. On Cox MVA, advanced age and non-lung metastases were associated with inferior OS (p < 0.03) with patients with 0–2 of these risk factors having estimated 2-year OS of 65.1 %, 38.9 %, and N/A, respectively. One- and 2-year LC rates were 85.3 % (95 % CI: 77.7–90.9 %) and 78.2 % (95 % CI: 67.9–85.6 %), respectively. On MVA, only BED4 < 175 Gy was associated with inferior LC (hazard ratio (HR) = 3.33; p = 0.01). Ten of 118 treated lesions had treatment-related toxicities (all Grade 1–2). ConclusionAge and lung vs. non-lung metastases were prognostic of OS and should be considered in patient selection for SABR. Dose escalation when feasible with BED4 ≥ 175 Gy is recommended given durable LC achieved without a subsequent increase in toxicity.