Abstract
PURPOSE: This study was designed to evaluate the relationship between the minimal margin size and local tumor progression (LTP) following CT-guided radiofrequency ablation (RFA) of colorectal cancer liver metastases (CLM). METHODS: An institutional review board-approved, HIPPA-compliant review identified 73 patients with 94 previously untreated CLM that underwent RFA between March 2003 and May 2010, resulting in an ablation zone completely covering the tumor 4-8 weeks after RFA dynamic CT. Comparing the pre- with the post-RFA CT, the minimal margin size was categorized to 0, 1-5, 6-10, and 11-15 mm. Follow-up included CT every 2-4 months. Kaplan-Meier methodology and Cox regression analysis were used to evaluate the effect of the minimal margin size, tumor location, size, and proximity to a vessel on LTP. RESULTS: Forty-five of 94 (47.9 %) CLM progressed locally. Median LTP-free survival (LPFS) was 16 months. Two-year LPFS rates for ablated CLM with minimal margin of 0, 1-5 mm, 6-10 mm, 11-15 mm were 26, 46, 74, and 80 % (p < 0.011). Minimal margin (p = 0.002) and tumor size (p = 0.028) were independent risk factors for LTP. The risk for LTP decreased by 46 % for each 5-mm increase in minimal margin size, whereas each additional 5-mm increase in tumor size increased the risk of LTP by 22 %. CONCLUSIONS: An ablation zone with a minimal margin uniformly larger than 5 mm 4-8 weeks postablation CT is associated with the best local tumor control.