Stereotactic body radiation therapy (SBRT) and radiofrequency ablation (RFA) are widely used therapies for the treatment of intrahepatic metastases; however, direct comparisons are lacking. We sought to compare outcomes for these 2 modalities.

From 2000 to 2015, 161 patients with 282 pathologically diagnosed unresectable liver metastases were treated with RFA (n = 112) or SBRT (n = 170) at a single institution. The primary outcome was freedom from local progression (FFLP). The effect of treatment and covariates on FFLP was modeled using a mixed-effects Cox model with application of inverse probability treatment weighting to adjust for potential imbalances in treatment modality.

The median follow-up period was 24.6 months. Patients receiving SBRT had larger tumors than those treated with RFA (median, 2.7 cm vs 1.8 cm; P < .01). On univariate analysis, tumor size was associated with worse FFLP for RFA (hazard ratio [HR]; 1.57; 95% confidence interval [CI], 1.15-2.14; P < .01) but not for SBRT (HR, 1.38; 95% CI, 0.76-2.51; P = .3). The 2-year FFLP rate was 88.2% compared with 73.9%, favoring SBRT (P = .06). For tumors ≥2 cm in diameter, SBRT was associated with improved FFLP (HR, 0.28; 95% CI, 0.09-0.93; P < .01). On multivariate analysis, treatment with SBRT (HR, 0.21; 95% CI, 0.07-0.62; P = .005) and smaller tumor size (HR, 0.65; 95% CI, 0.47-0.91; P = .01) were associated with improved FFLP. The 2-year overall survival rate was 51.1%, with no difference between groups (P = .8). Grade ≥3 treatment-related toxicity was rare, with no difference between SBRT (n = 4) and RFA (n = 3).

Treatment with SBRT or RFA is well tolerated and provides excellent and similar local control for intrahepatic metastases <2 cm in size. For tumors ≥2 cm in size, treatment with SBRT is associated with improved FFLP and may be the preferable treatment.