CT-Based Quantification of Tissue Shrinkage in Thermal Ablation of Hepatocellular Carcinoma

Abstract

Background: Tissue shrinkage is a poorly understood phenomenon that might occur during thermal ablation (TA) of hepatocellular carcinoma (HCC). It may lead to underestimation of the minimal ablation margin (MAM), a key determinant of technical success of TA.
Objective: The objective of this study was to explore three computed tomography (CT) based methods to quantify tissue shrinkage in TA of HCC: marker-based, vessel-based, and image-based.
Methods: This single-centre study used immediate pre- and post-ablation contrast-enhanced computed tomography (CECT) scans from the prospective PROMETHEUS database. Patients were treated in the Leiden University Medical Center (LUMC) with radiofrequency ablation (RFA) or microwave ablation (MWA) and scanned during high-frequency jet ventilation (HFJV) or during apnoea. Patients with < 5 mm of craniocaudal liver displacement were included in this study. Mean distance between landmarks on pre-ablation scans was compared to that on post-ablation scans for the marker-based quantification. Mean difference between pre- and post-ablation vessel tree to ablation surface was compared for the vessel-based quantification. The image-based method used Jacobian determinant (JD) analysis to quantify voxel-wise volume changes.
Results: 10 patients with a total of 12 tumours were included in this study. Mean (standard deviation, SD) marker-based shrinkage was -1.24 (2.45) mm. Median (interquartile range, IQR) difference in vessel-to-ablation distance between pre- and post-ablation vessels within the ablation zone and a 10-mm margin was 0.07 (-0.08–0.11) mm. The image-based quantification method yielded a median (IQR) JD value of 1.01 (0.98–1.02), indicating a 1% increase in volume in the ablation zone and a 10-mm margin.
Conclusion: Based on the study results, no conclusions can be drawn on whether tissue shrinkage occurs in vivo. Clinical use of the CT-based quantification methods described in this study is limited by validation challenges. Future work should start with establishing a ground truth for tissue shrinkage.