Effectiveness of radiofrequency ablation for lipiodol-chemoembolized hepatocellular carcinoma is predictable by intraoperative impedance monitoring

[Purpose] We herein report that effectiveness of radiofrequency ablation (RFA) for lipiodol-chemoembolized hepatocellular carcinoma (HCC) is predictable by intraoperative impedance monitoring. [Subjects and methods]We studied 18 cases of hepatocellular carcinoma, where the HCC was treated initially with lipiodol-chemoembolization (Lp-TACE) and subsequently with percutaneous RFA. RFA was performed using the Cool tip type RFA system, which could allow intraoperative monitoring of the changes in the impedance of tumor nodules. The size of the HCC ranged from 6 to 41 mm (17.6+/-13 mm). The efficacy of RFA was estimated using enhanced CT on day 1 to 3. [Results] The 18 HCC nodules were divided into 2 groups according to the difference in the chronologic changing pattern of impedance following the initial break. In group-1 (n=10), the impedance dropped or did not change from the level at the initial break. In contrast, in group-2 (n=8), it increased. In group-1, the electrode temperature at the end of ablation was at 76.6+/-7.8°C, and 9 of 10 HCC nodules could obtain an ample safety margin (SM) around the lipiodol accumulated area. On the other hand, in group-2, its temperature was 67.0+/-3.9°C, which was significantly lower than that of group-1 (p<0.001), and its SM was insufficient. The width of SM was neither correlated to the size of HCC nor the length of electrode. [Conclusion] When applying RFA after Lp-TACE, the ablation effect can therefore be predicted by monitoring the impedance during radiofrequency ablation, especially following the initial break.