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 vivoefficacy of radiofrequency ablation (RFA) in porcine liver usingOctopus® electrodes for creating a large coagulation compared with RFAusing clustered electrodes.

Methods

A total of 39 coagulations were created using a 200-W generator and clusteredelectrodes or Octopus electrodes during laparotomy in 19 pigs. Radiofrequencywas applied to the livers using four protocols: (1) Group A-1, monopolarmode 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 cmand 33.1 cm³, respectively) were significantly larger thanthose 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 GroupB-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 vs30.2 cm³, respectively (p<0.05).The energy efficiencies were also significantly higher in Groups A-2 and B-2than in Groups A-1 and B-1 (p<0.05).

Conclusion

The Octopus electrodes were more efficient for creating a large ablationzone than clustered electrodes, and the efficacy of RFA with Octopus electrodescan 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 acceptanceas a valuable, minimally invasive treatment for primary and secondary livermalignancies [1]. Comparedwith conventional surgery, RF ablation (RFA) has many advantages in termsof reduced complications, morbidity and mortality as well as its cost-effectiveness.However, a major obstacle preventing the widespread use of RFA is its inabilityto reliably create adequate volumes of complete tumour destruction with sufficientsafety margins, thus causing an increasing rate of marginal recurrence inlarge tumours due to the incomplete RFA. Most clinically available electrodes,including internally cooled electrodes, clustered electrodes, multitined expandableneedle electrodes and perfusion electrodes, can induce coagulation necrosisin 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 overlappingablations are often required to cover the entire tumour volume as well asthe peripheral ablation margins [4,5]. However, in clinical practice, thereis considerable difficulty repositioning the probe under ultrasound guidanceduring overlapping ablations as numerous microbubbles form in the heated tissueduring RFA and may thus interfere with finding the electrode tip and the untreatedportions of the target tumour on ultrasound [6].In order to avoid problems related to multiple overlapping ablations, includingtechnical difficulties and a long procedure time, several approaches havebeen used to treat medium and large liver tumours. These include the use ofcluster electrodes [7], multitinedelectrodes with saline infusion (RITA Medical Systems, Mountain View, CA) [2] and multiple electrodes in the switchingmonopolar mode or multipolar mode [8-11].Although several previous studies demonstrated that the use clustered electrodesor multiple electrodes in the switching or multipolar modes could create largercoagulations [2,3,6,8-14], they also presented several potential unsolvedproblems. The clustered electrode problems include: (1) convergence of thethree individual needles <5 mm; (2) limited access to the target tumourowing to narrow intercostal spaces; and (3) displacement of the liver dueto its resistance to the electrode. Although RFA using multiple electrodescan successfully treat large liver tumours, it is still not widely used inclinical practice, primarily owing to its high cost and the complexity ofusing multiple electrodes.Recently, in order to improve the efficiency of clustered electrodes increating a large ablation zone and to diminish any potential problems, wedeveloped a separable clustered electrode (Octopus®; Taewoong MedicalCo., Ltd, Goyang, Republic of Korea) with a specialised handle that can beincorporated into a larger handle in a single unit (Figure1). Our electrode can be placed as a single electrode with variableinterelectrode distances, according to the shape and size of the target tumour,or in a similar way to the clustered electrodes that are also composed ofthree electrodes as a single body at a fixed 5-mm interelectrode distance.Therefore, prior to their clinical application, we attempted to prove the invivo efficacy of RFA using the Octopus electrodes to create a largearea of coagulation necrosis in either the conventional or switching monopolarmode 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 toone port. (d) An illustration, which shows details of the connection betweenthe needles and radiofrequency (RF) ablution system in a three Octopus electrodessystem.