Safety margin assessment after microwave ablation of liver tumors: inter- and intrareader variability

Abstract

Objective:To evaluate the inter- and intrareader variability of the safety margin assessment after microwave ablation of liver tumors using post-procedure computed tomography (CT) images.

Methods:A retrospective analysis of 58 patients who underwent MWA of primary or secondary liver malignancies (46 hepatocellular carcinoma, 9 metastases of a colorectal cancer and 3 metastases of pancreatic cancer) between September 2017 and June 2019 was conducted. Three readers estimated the minimal safety margin in millimeters using side-by-side comparison of the 1-day pre-ablation CT and 1-day post-ablation CT and judged whether ablation was complete or incomplete. One reader estimated the safety margin again after 6 weeks. The aim was to detect inter- and intrareader differences as well as to determine the sensitivity and specificity of identification remnant tumor tissue. Magnetic resonance imaging (MRI) after 6 weeks was the gold standard. 

Results: The intraclass correlation coefficient (ICC) for estimation of the minimal safety margin of all three readers was 0.357 (95%-confidence interval 0.194 - 0.522). The ICC for repeated assessment (reader 1) was 0.774 (95%-confidence interval 0.645 - 0.860). Sensitivity and specificity of the detection of complete tumor ablation, defined as no remnant tumor tissue in 6 weeks follow-up MRI, was 93%/82%/82% and 33%/17%/83%.

Conclusion: In clinical practice the safety margin after liver tumor ablation is often assessed using side-by-side comparison of CT images. In our study we were able to show, that this technique has a poor reliability (ICC 0.357). From our point of view, this proves the necessity of new technical procedures for the assessment of the safety distance.