Stereotactic ablative radiation therapy for extracranial metastases from malignant melanoma: An international multi-institutional analysis.

Objective: To report on local control (LC), toxicity, and overall survival (OS) following stereotactic ablative radiation therapy (SABR) for extracranial metastases from malignant melanoma.

Methods: The RSSearch^® Patient Registry was searched for patients with extracranial melanoma metastases treated with SABR. LC was defined as the time from completion of SABR to the date of last radiographic follow-up with either stability or decrease in size of the treated metastasis or the date at which lesion growth was radiographically confirmed per RECIST criteria. Kaplan-Meier analyses were utilized to evaluate potential prognostic factors on univariate analyses (UVA) with log-rank tests followed by use of a Cox proportional hazards multivariate (MVA) model.

Results: There were 45 patients with 52 extracranial melanoma metastases treated with SABR. One- and 2-year LC rates were both 85.3% (95% CI: 67.9-93.7%) following SABR. On UVA, BED10 < 60 Gy was associated with poorer 1-year and 2-year LC (96% vs. 61.9%), which remained significant on MVA (hazard ratio [HR] = 7.06; p = 0.03). On UVA, pulmonary vs. non-pulmonary metastases were correlated with 1-year OS (84.5% vs. 57.4%; p = 0.05) and non-spinal vs. spinal metastases (74.3% vs. 56.3%; p = 0.02), though neither were significant on MVA. The incidence of treatment-related toxicity was 18.9%, all Grade 1-2.

Conclusion: We recommend dose/fractionation schedules that meet or exceed BED10 ≥ 60 Gy when treating extracranial melanoma metastases with SABR.