Thermal ablation of primary liver tumors: Correspondence of the predicted ablation zone with the clinically obtained ablation zone

Abstract

Purpose Manufacturer’s predictions of ablation zone dimensions are the current directives for treatment planning in thermal ablation, while they are mostly based on ex vivo experiments making its reliability questionable. The aim of this study is to determine the correspondence in dimensions, volume, shape and overlap of the manufactures’ predicted with the clinically realized ablation zones following thermal ablation of hepatocellular carcinoma (HCC). The secondary objective is to determine the effect of tumor- and liver characteristics on this correspondence.
Methods Data was retrospectively collected from two prospective studies. A registered pre-ablation and post-ablation computed tomography scan with liver, tumor and ablation zone segmentations were available for analysis. Needle position reconstruction was performed based on image visual assessment (e.g., gas formation, tumor location and subcapsular hemorrhage) using in-house developed software. The dimensions of the predicted ablation zone were derived from the manufacturer’s chart corresponding to treatment settings used during ablation. The long axis diameter (LAD), short axis diameter (SAD) and volume of the realized and predicted ablation zone were compared. The overlap was determined using the Dice similarity coefficient (DSC) and the average surface deviation between the realized and predicted ablation zone. The effect of tumor location, vascular proximity and liver cirrhosis on the overlap was quantified using the DSC and average surface deviation.
Results Nineteen patients and 21 ablations were included for analysis. The median realized volume did not significantly differ from the predicted volume, 25.7 cm3 and 22.6 cm3 respectively (p = 0.526). The median LAD and SAD of the realized ablation zone differed significantly from the manufacturer’s prediction (51.9 mm vs 40.0 mm, p<0.001 and 36.9 mm vs 35.0 mm, p<0.001 respectively). The predicted ablation zone corresponds to the realized ablation zone with a mean DSC of 0.73 and mean average surface deviation of 3.04 mm. Tumor location and vascular proximity did not affect the overlap between the realized and predicted ablation zone. The effect of liver cirrhosis was not assessed due to a low sample size of HCC in a non-cirrhotic liver (n=2).
Conclusion The manufacturer’s predicted volume of liver ablation zones corresponds well to the clinically realized ablation volume. However, the LAD and SAD are underestimated by the manufacturers. The shape and overlap of the predicted and realized ablation zone were sufficient. Further studies evaluating the effect of tumor- and liver characteristics on the correspondence of the predicted with the realized ablation zone with a larger patient cohort is needed.