Utility of computed tomography fusion imaging for the evaluation of the ablative margin of radiofrequency ablation for hepatocellular carcinoma and the correlation to local tumor progression

Aim To demonstrate the usefulness of the computed tomography (CT) fusion imaging for the evaluation of treatment effect of radiofrequency ablation (RFA) for hepatocellular carcinoma (HCC). Methods Eighty‐five patients with 94 HCC with complete ablation judged on conventional side‐by‐side interpretation of pre‐RFA and post‐RFA CT at the time of RFA were included in this retrospective study. CT data was retrospectively used to create fusion images of pre‐RFA and post‐RFA CT using automatic rigid registration and manual correction referring to intrahepatic structures and hepatic contours around a tumor. Clinical factors including a minimal ablative margin (MAM) measured on fusion images were examined to prove risk factors for local tumor progression (LTP). Results LTP was observed in 13 (13.8%) tumors with a median follow up of 21.0 months (range, 2–75). The mean MAM on the fusion image was 1.4 ± 3.1 mm and 23 tumors (24.5%) were judged to be protruding from the ablation zone. Multivariate analysis revealed that protruding from the ablation zone was the only significant factor for LTP (hazard ratio, 7.09; 95% confidential interval, 2.26–22.3; P