# Intraoperative Radiofrequency Ablation Using a Loop Internally Cooled-Perfusion Electrode: In Vitro and In Vivo Experiments (2022)

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## Journal of Surgical Research

Volume 131, Issue 2,

April 2006

, Pages 215-224

### Objective

We sought to validate the efficiency of intraoperative radiofrequency ablation (RFA) using a prototype loop internally cooled-perfusion (LICP) electrode to induce coagulation in the subcapsular portion of the liver.

### Materials and methods

In in vitro experiments, 30 ablation regions were created using a 200-W generator and a LICP electrode featured simultaneous intraelectrode cooling and continuous flow of hypertonic saline along the shaft in explanted bovine liver. In the in vivo experiments, 26 ablation zones were created according to one of the five protocols in 10 dogs: group A, RFA using a cooled-tip electrode (n = 6); group B, RFA using a LICP electrode with 2 cm loop tip (n = 6); group C, RFA using a LICP electrode with a 3-cm loop tip (n = 6); group D, RFA using a cooled-tip electrode and Pringle maneuver (n = 4); and group E, RFA using a LICP electrode with 2 cm loop tip and Pringle maneuver (n = 4). The dimensions of the coagulation parameters were compared between the groups.

### Results

In the in vitro experiments, RFA using a 2- or 3-cm diameter LICP electrode (3.6 ± 0.3 cm, 3.4 ± 0.5 cm, respectively) created deeper dimensions of coagulation than did a 4-cm electrode (2.3 ± 0.2 cm; P < 0.05). In the in vivo experiments, the RFA using the LICP electrodes in porcine liver with normal perfusion induced wider but superficial ablation regions when compared to standard RFA using an internally cooled electrode (P < 0.05). However, using a Pringle maneuver, RFA with a LICP electrode created a larger volume of ablation area when compared to RFA using an internally cooled electrode with a similar range of axial diameter along the electrode axis: 30.0 ± 6.1 cm3 (group D) versus 68.5 ± 14.0 cm3 (group E; P < 0.05)

### Conclusions

Intraoperative RFA using the LICP electrode induced a well-defined semicircular coagulation with a 3.5-cm axial diameter in the subcapsular region of the liver. This device appears to be promising for the treatment of superficial tumors during intraoperative RFA.

## Introduction

Radiofrequency ablation (RFA) has gained wide acceptance as a minimally invasive local tumor ablative therapy for the treatment of primary and secondary liver malignancies [1, 2, 3, 4]. In addition, the promising results from studies regarding the use of percutaneous RFA have demonstrated that combined treatment with RFA and anatomical hepatectomy and/or wedge resections by radiologists and surgeons is increasingly used in clinical care [5, 6, 7, 8, 9, 10]. Combined RFA with partial hepatectomy is considered an option when multiple liver metastases are identified in both lobes of the liver at surgery [7, 8, 9, 10]. Indeed, this combined therapeutic strategy expands the indication for hepatic resection for liver malignancies. Furthermore, this approach provides a potentially curable therapeutic option for those patients with multiple metastases to both lobes of the liver.

However, although intraoperative RFA, using the standard commercially available electrode, is considered to be effective for treating centrally sited, spherical shaped, small metastases in the liver, it may not be well suited for superficially located tumors with wide transverse diameter because the diameter of the RF ablation zone perpendicular to the electrode axis usually is not as large as the diameter along the electrode axis [11]. Although fulguration of the hepatic surface tumors using a Bovie electrocautery unit is a well-established technique for surgeons, the depth of tissue destruction has been limited to a few millimeters because of charring of the surface at the point of electrode contact [12, 13, 14].

In our institute, approximately 30% of hepatic RFA procedures for the treatment of primary and secondary liver tumors were performed at laparotomy. From our experience using intraoperative RFA for treating hepatic metastases, it is quite uncommon to treat superficially located liver metastases with RFA. Given the shape of the ablation zone created by the standard needle type, the RF electrode is not optimal for treating oval-shaped, superficially located tumors. Therefore, we developed a prototype electrode with a loop-shaped active tip. To prevent charring at the electrode-tissue contact area, the electrode provides a continuous flow of saline, which has the effect of a good coolant and electrical conductor [15, 16].

The purpose of this study was to determine whether RFA using a prototype loop internally cooled-perfusion LICP electrode could create larger subcapsular ablation zone in the liver when compared with RFA using a standard needle electrode.

## Design of LICP Electrode

We developed a LICP electrode with the use of previous studies for reference [17, 18, 19]. It was assumed that simultaneous intraelectrode cooling and continuous saline flow along the electrode shaft during RFA are both necessary to avoid charring of the surface at the point of electrode contact. Our goal was to develop a 17-gauge internally cooled electrode with an active loop that was covered with a 15-gauge outer metallic sheath. First, we modified a 17-gauge, internally cooled electrode

## The Effect of Loop Size of the Electrode on the Dimension of Ablation Zone

During RFA using the LICP electrodes, the impedance was gradually decreased to 50–60 Ω and the mean delivered RF energy was 105 7 ± 18 kJ. After RFA, a well-defined area with a central white discoloration was observed in the ablated zone (Fig. 2). RFA using a 2- or 3-cm diameter LICP electrode (3.6 ± 0.3 cm, 3.4 ± 0.5 cm, respectively) created a deeper dimension of coagulation than did a 4 cm diameter electrode (2.3 ± 0.2 cm; P < 0.05; Table 1). However, there were no significant differences in

## Discussion

Surgeons use fulguration of surface tumors with RF electrocautery devices. However, the depth of tissue destruction has been limited to a few millimeters because of charring at the surface point of electrode contact. For patients with multiple tumors, including tumors larger than 4–5 cm, a combined treatment approach including surgical resection for the large tumors and RFA for smaller lesions may provide a valuable therapeutic option with the potential for cure [7, 8, 9, 10]. Currently, for

## Acknowledgments

This study was supported by grant no. 21-2005-021-0 from the Seoul National Research University Fund.

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• ## Cited by (3)

• Radiofrequency ablation with monopolar cluster versus bipolar multipolar electrodes for the ablation of ⩾2.5cm hepatocellular carcinoma

2016, Egyptian Journal of Radiology and Nuclear Medicine

To compare the effectiveness of radiofrequency ablation using a monopolar cluster and a bipolar multipolar electrode for the ablation of (⩾2.5cm) hepatocellular carcinoma.

34 patients with a single HCC (mean size, 4.46±2.3cm; range, 2.5–7.4cm) underwent percutaneous RFA with monopolar cluster (n=18) or bipolar multipolar electrodes (n=16). Technical success, technical effectiveness, major complications, and tumor progression were compared.

Technical success was achieved in 83, 3%, and 81.3% of patients in the monopolar cluster and bipolar multipolar group respectively. Technical effectiveness was achieved in 87.5% and 94.4% of patients treated by monopolar cluster electrodes and bipolar multipolar electrodes, respectively (P=0.591). No major complications were developed. Follow-up mean period was 21.4months. The median local tumor progression rates were 17.7and 22.7months in the monopolar cluster and bipolar multipolar group respectively. On multivariate analysis, the use of a monopolar cluster electrode (P=0.239) was risk factor for complication.

There were no differences in terms of complete ablation, local tumor progression, distant recurrence, and complication rates, but the overall survival regarding the distant recurrence and the life expectancy is better in bipolar multipolar electrodes compared to the monopolar cluster electrodes.

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