Comparison of therapeutic efficacy and safety of radiofrequency ablation of hepatocellular carcinomas between internally cooled 15-G and 17-G single electrodes

Objective:

To compare the ablation volume, local tumour progression rate and complication rate of radiofrequency ablation (RFA) for small hepatocellular carcinomas (HCCs) using 15-G and 17-G single electrodes.

Methods:

This retrospective study was approved by the institutional review board and informed consent was waived. We reviewed percutaneous RFA cases for HCCs using 15-G or 17-G electrodes without multiple overlapping ablations. A total of 36 pairs of HCCs matched according to tumour size and active tip length were included. We compared ablation volume and complication rate between the two electrode groups. Cumulative local tumour progression rates were estimated using the Kaplan–Meier method and compared using the log-rank test.

Results:

Tumour size and ablation time were not significantly different between the 15-G and 17-G groups (p = 0.661 and p = 0.793, respectively). However, ablation volume in the 15-G electrode group was larger than that in the 17-G group (14.4 ± 5.4 cm³ vs 8.7 ± 2.5 cm³; p < 0.001). No statistical difference in complication rates between the two electrode groups was found. The 10- and 20-month local tumour progression rates were not significantly different between the two groups (2.8% and 5.6% vs 11.1% and 19.3%; p = 0.166).

Conclusion:

Ablation volume by the 15-G electrode was larger than that by the 17-G electrode. However, local tumour progression rate and complication rate were not significantly different between the two electrode groups.

Advances in knowledge:

RFA of HCC using a 15-G electrode is useful to create larger ablation volumes than a 17-G electrode.Radiofrequency ablation (RFA) is now considered to be one of the curative treatment modalities for the management of small hepatocellular carcinomas (HCCs).^1–5 There are various types of electrodes for RFA, including internally cooled electrodes, multi-tined electrodes and perfusion electrodes.^6,7 Among them, an internally cooled electrode is frequently used because it is simple and easy to use. The ablation zone created by an internally cooled electrode is usually cylindrical in shape along the longitudinal axis of the electrode. Hence, the horizontal diameter of the ablation zone is relatively smaller than the longitudinal diameter. Therefore, an internally cooled electrode frequently requires overlapping ablations to achieve a sufficient ablative margin for large tumours (i.e. size >2.5 cm). However, it is sometimes technically difficult to achieve a sufficient ablative margin under ultrasonography guidance since both the boundary of the index tumour and the active tip of the electrode are obscured by the echogenic zone generated by the previous ablation cycle. Therefore, it is ideal to achieve a large ablation zone using a single electrode without multiple overlapping ablations.Electrodes with a larger diameter have a larger contact surface with the surrounding tissue than smaller ones and thereby have a higher active electric field.^8–10 This in turn delivers a larger amount of radiofrequency energy and thus produces a greater amount of heat around the active tip. Consequently, large electrodes create large ablation zones. However, to our knowledge, commercially available internally cooled electrodes are not large and are almost exclusively 17-G.^11,12Recently, larger sized 15-G electrodes have been introduced and used for RFA of liver tumours in our institution. We have found that the 15-G electrode created a larger ablation volume than did the 17-G electrode, while the complication rate differed little. However, to our knowledge, there are no comparative data in the literature regarding the therapeutic efficacy and complication rate after RFA between 15-G and 17-G single electrodes. Hence, the purpose of this study was to evaluate and compare the ablation volume, local tumour progression rate and complication rate after RFA of HCCs using 15-G and 17-G single electrodes.