Multiple-electrode radiofrequency ablations using Octopus(R)electrodes in an in vivo porcine liver model

Objectives

The objective of this study was to determine the in vivo efficacy of radiofrequency ablation (RFA) in porcine liver using Octopus® electrodes for creating a large coagulation compared with RFA using clustered electrodes.

Methods

A total of 39 coagulations were created using a 200-W generator and clustered electrodes or Octopus electrodes during laparotomy in 19 pigs. Radiofrequency was applied to the livers using four protocols: (1) Group A-1, monopolar mode using a clustered electrode (n=11); (2) Group A-2, monopolar mode using an Octopus electrode (n=11); (3) Group B-1, consecutive monopolar mode using three, clustered electrodes (n=8); and (4) Group B-2, switching monopolar mode using two Octopus electrodes (n=9). The energy efficiency, shape, diameters (D) and volume (V) of the coagulation volume were compared in each of the two groups.

Results

The mean maximum D and V of the coagulations in Group A-2 (4.7 cm and 33.1 cm³, respectively) were significantly larger than those in Group A-1 (4.1 cm and 20.3 cm³, respectively) (p<0.05). Furthermore, the mean minimum D, maximum D and V of the coagulations in Group B-2 were significantly larger than those in Group B-1, i.e. 5.3 vs 4.0 cm, 6.6 vs 4.9 cm and 66.9 vs 30.2 cm³, respectively (p<0.05). The energy efficiencies were also significantly higher in Groups A-2 and B-2 than in Groups A-1 and B-1 (p<0.05).

Conclusion

The Octopus electrodes were more efficient for creating a large ablation zone than clustered electrodes, and the efficacy of RFA with Octopus electrodes can be amplified in the switching monopolar mode.In recent years, image-guided percutaneous tumour ablation using radiofrequency (RF) energy has become increasingly popular and has gained wide acceptance as a valuable, minimally invasive treatment for primary and secondary liver malignancies 1]. Compared with conventional surgery, RF ablation (RFA) has many advantages in terms of reduced complications, morbidity and mortality as well as its cost-effectiveness. However, a major obstacle preventing the widespread use of RFA is its inability to reliably create adequate volumes of complete tumour destruction with sufficient safety margins, thus causing an increasing rate of marginal recurrence in large tumours due to the incomplete RFA. Most clinically available electrodes, including internally cooled electrodes, clustered electrodes, multitined expandable needle electrodes and perfusion electrodes, can induce coagulation necrosis in the range of 3–4 cm in diameter after a single ablation session 2,3]. Therefore, to treat liver tumours >3 cm in diameter, multiple overlapping ablations are often required to cover the entire tumour volume as well as the peripheral ablation margins 4,5]. However, in clinical practice, there is considerable difficulty repositioning the probe under ultrasound guidance during overlapping ablations as numerous microbubbles form in the heated tissue during RFA and may thus interfere with finding the electrode tip and the untreated portions of the target tumour on ultrasound 6].In order to avoid problems related to multiple overlapping ablations, including technical difficulties and a long procedure time, several approaches have been used to treat medium and large liver tumours. These include the use of cluster electrodes 7], multitined electrodes with saline infusion (RITA Medical Systems, Mountain View, CA) 2] and multiple electrodes in the switching monopolar mode or multipolar mode 8-11]. Although several previous studies demonstrated that the use clustered electrodes or multiple electrodes in the switching or multipolar modes could create larger coagulations 2,3,6,8-14], they also presented several potential unsolved problems. The clustered electrode problems include: (1) convergence of the three individual needles <5 mm; (2) limited access to the target tumour owing to narrow intercostal spaces; and (3) displacement of the liver due to its resistance to the electrode. Although RFA using multiple electrodes can successfully treat large liver tumours, it is still not widely used in clinical practice, primarily owing to its high cost and the complexity of using multiple electrodes.Recently, in order to improve the efficiency of clustered electrodes in creating a large ablation zone and to diminish any potential problems, we developed a separable clustered electrode (Octopus®; Taewoong Medical Co., Ltd, Goyang, Republic of Korea) with a specialised handle that can be incorporated into a larger handle in a single unit (Figure 1). Our electrode can be placed as a single electrode with variable interelectrode distances, according to the shape and size of the target tumour, or in a similar way to the clustered electrodes that are also composed of three electrodes as a single body at a fixed 5-mm interelectrode distance. Therefore, prior to their clinical application, we attempted to prove the in vivo efficacy of RFA using the Octopus electrodes to create a large area of coagulation necrosis in either the conventional or switching monopolar mode compared with RFA using a clustered electrode in porcine liver.Open in a separate windowFigure 1(a,b) Photographs of the Octopus® electrodes (Taewoong Medical Co., Ltd, Goyang, Republic of Korea), all of which have three individual needles. (c) Adaptor for the Octopus electrodes which connects the three cables to one port. (d) An illustration, which shows details of the connection between the needles and radiofrequency (RF) ablution system in a three Octopus electrodes system.