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

Background: We aimed to characterize local control (LC) and overall survival (OS) following stereotactic ablative radiation therapy (SABR) for extracranial sarcoma metastases.Methods: A 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.Results: A 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 Gy(4) (range56.3 Gy(4)-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).Conclusion: Age 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.