Guidelines for power and time variables for microwave ablation in a porcine liver.

The purpose of our study was to provide guidelines for the use of a novel microwave ablation system. Microwave ablations using a 915-MHz system were evaluated in a porcine liver. The independent variables were power and time, with the outcome variable being diameter of ablation. After ablations, livers were procured for measurement and histologic evaluation. Our study consisted of 420 ablations. The outcome variable, ablation diameter, was affected significantly by time, power, and time/power interaction (p<0.0001). For each time point, a one-way analysis of variance (ANOVA) showed an overall significant difference in ablation size X wattage (p<0.0001). Tukey tests at each time point showed ablation sizes at 45, 50, and 60 W were not significantly different. After it was determined that 45 W was optimal, a one-way ANOVA showed an overall significant difference in ablation sizes for time points at 45 W (p<0.0001). Tukey tests revealed that at 45 W, ablation sizes at 10, 15, and 20 min were not statistically different. We propose guidelines for diameters based on different time and power variables and recommend 45 W for 10 min to achieve optimal diameters at the shortest time and lowest wattage.