Effects of lipiodol uptake on ablation zone size following combined transarterial embolization and microwave ablation of hepatocellular carcinoma

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Purpose :
To evaluate the effects of lipiodol uptake and density on ablation zone size following combined transarterial embolization (TACE) and microwave ablation (MWA) of hepatocellular carcinoma (HCC).
Materials & Methods :
A total of 14 patients were identified from 12/2017-2/2021 who underwent combined TACE+MWA for HCC. All ablations conformed to exact manufacturer protocols: 1 Neuwave PR probe at 65W for 5 min or 1-2 PR probe(s) at 65W for 10 min. Ablation durations that deviated from 5 or 10 min were excluded. TACE was performed with chemolipiodol emulsion only and followed by MWA the next day. Unenhanced CT scan from immediate post TACE and enhanced 1-month post-MWA CT scan were analyzed. Post-MWA CT images during portal or venous phase were converted to isotropic volumes (1x1x1 mm), and ablation zones were manually segmented. Ratios of ablation volumes to manufacturer specifications, based on ellipsoid formula, were calculated and compared using Welch’s t-test. Post-TACE CT scan was semi-automatically registered to post-MWA CT using affine transformation and mutual information via ITK-SNAP. The segmented ablation volumes were then used to quantify lipiodol uptake present on the post-TACE CT. Lipidol density was measured by average Hounsfield units within the segmented volume divided by the total ablation volume. Linear regression was performed between lipiodol density and ratio of ablation zones, and correlation coefficients determined.
Results :
No significant difference in ablation volumes were seen following TACE with chemolipiodol emulsion compared to manufacturer specifications. Although there was a trend towards smaller ablation volume ratios with 10 min durations compared to 5 min, this was not statistically significant (0.87±0.29 vs 1.16±0.31, respectively, p=0.09). There was poor linear correlation between lipiodol density to ablation volume ratio (r=-0.20, r2=0.04).
Conclusions :
In this retrospective study, no significant difference was seen in ablation volumes following TACE with chemolipiodol emulsion only. The high boiling point of lipiodol (125C) compared to blood, and low thermal conductivity of lipiodol may preclude the additive or synergistic effects of TACE on ablation volumes that are typically seen following substitution or supplementation with particle embolization. Unless very high temperatures are consistently obtained, the presence of chemolipidol alone does not appear to promote a synergistic and “deep-frying” phenomenon during MWA of HCC.
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Associated Sessions

Assistant Professor
Oregon Health & Science University
Catlin Gabel School
Oregon Health & Science University

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