342 - Determination of Ablation Zone Size in Swine Cirrhosis Model

Purpose: Complete ablation requires accurate ablation zone size prediction to cover the lesion and a margin. Most manufacturers provide ablation zone sizes by wattage and time based on ablation performed in healthy tissue without underlying disease. The goal of this study was to determine the size of the ablation zone in a large animal cirrhosis model to see how cirrhosis would affect the ablation size.

Materials and Methods: Cirrhosis was induced in swine using intra-arterial hepatic injection of ethanol and ethiodized oil mixture 1:3 as previously described under anesthesia. After 6-8 weeks post induction procedure, swine underwent microwave ablation under anesthesia. Using ultrasound guidance, 4 ablations were performed on each pig with various parameters using the Intelliblate Ablation System (Varian Medical Systems, Inc). Four settings were tested (90 W×10 min, 30 W×10 min, 90 W×5 min, 30 W×5 min)

Ablation zone sizes were measured on ultrasound. Ablation zone dimensions (X (cm), Y (cm)) and area (cm²) were measured in cirrhotic liver tissue and compared to expected values based on normal hepatic animal models.

Euthanasia was performed either immediately post ablation or 2 weeks post ablation to assess acute vs chronic changes. Ablation zones were examined on specimens with gross visualization and H&E examination as well as TUNEL.

Statistical analysis was conducted using a two-tailed, two-sample equal variance T-test to compare expected versus observed ablation parameters.

Results: In total, 17 ablations were performed on 4 pigs across the four settings. The ablation zones in cirrhotic livers were consistently smaller than the expected values calculated based of in-vivo swine liver model. The difference in ablation size was up to 28% smaller in 90W*10min (p0.014) and 26% for 30W*5 min (p=0.05). The ablation size of cirrhotic liver showed a tendency to be up to 13% smaller vs. normal liver for 30W*10min and 90W*5min but those differences were not statistically significant.

Conclusion: In these cirrhotic swine models produced smaller ablation zones compared to manufacturer provided ablation zone based on healthy swine liver. Despite small sample size, these findings were significant for 90W*10min and 30W*5min parameters. These results suggest that ablation zone sizes provided by manufacturers should be adjusted based on underlying liver disease and parameters need to be adjusted to obtain the same ablation size as a normal liver.