A multi‐step, incremental expansion method for radio frequency ablation: optimization of the procedure to prevent increases in intra‐tumor pressure and to reduce the ablation time

BACKGROUND/AIMS: Radio frequency ablation (RFA) has been accepted clinically as a useful local treatment for hepatocellular carcinoma (HCC). However, intra-hepatic recurrence after RFA has been reported. We initially hypothesized that recurrence was attributable to increases in intra-tumor pressure during RFA, and we subsequently measured the pressure and optimized the procedure. METHODS: A block of pig liver sealed in a rigid plastic case was used as a model of an HCC tumor with a capsule. We compared the pressure between a single-step full expansion of the needle (single-step method) and incremental, stepwise expansion (multi-step method), and evaluated the effect of varying the electrical power. Finally, we performed a preliminary comparison of the ablation times for these methods in HCC cases. RESULTS: The multi-step method resulted in a significantly lower pressure and shorter total ablation time than the single-step method. Furthermore, incremental expansion in 10 steps resulted in a lower pressure and shorter ablation time than four steps. Seventy W-ablation resulted in a lower pressure and shorter time than 30- or 50 W-ablation. In HCC cases, the multiple-step method had a significantly shorter ablation time than the single-step method. CONCLUSION: The multi-step method can be recommended to reduce the ablation time, and suppress the increase in pressure.