Radiofrequency ablation of large size liver tumours using novel plan-parallel expandable bipolar electrodes: Initial clinical experience

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Abstract

Purpose

Although radiofrequency ablation (RFA) is a promising method for local treatment of liver malignancies, with conventional monopolar systems recurrence rates for large size tumours (≥3.5 cm) remain high. The objective of this study was to evaluate the safety, feasibility and local effectiveness of a novel bipolar plan-parallel expandable system for these larger tumours.

Methods and materials

Eight consecutive patients with either unresectable colorectal liver metastases (CRLM in 6 patients), carcinoid liver metastases (1 patient) and hepatocellular carcinoma (HCC in 1 patient) of ≥3.5 cm were treated with bipolar RFA during laparotomy with ultrasound guidance. Early and late, major and minor complications were recorded. Local success was determined on 3–8 month follow-up CT scans of the upper abdomen.

Results

Nine CRLM, one carcinoid liver metastases and one HCC (3.5–6.6 cm) were ablated with bipolar RFA. Average ablation time was 16 min (range 6–29 min.). Two patients developed a liver abscess which required re-laparotomy. In both cases bowel surgery during the same session probably caused bacterial spill. There were no mortalities. The patients were released from hospital between 5 and 29 days after the procedure (median 12 days). The 6–12 month follow-up PET-CT scans showed signs for marginal RFA-site tumour recurrence in three patients with CRLM (3/11 lesions).

Conclusion

Preliminary results suggest bipolar RFA to be a reasonably safe, fast and feasible technique which seems to improve local control for large size hepatic tumour ablations.

Introduction

Currently, the most widely used tumour ablative technique for treatment of liver malignancies is radiofrequency ablation (RFA). In patients with unresectable hepatic tumours RFA has proven to be safe and feasible [1], [2]. Furthermore, RFA has been suggested to improve both short and long term survival [3]. Unfortunately, 8–40% of treated patients have local RFA-site tumour recurrence, especially in tumours ≥3.5 cm in diameter [4], [5], [6].

In conventional “monopolar” RFA an active electrode is placed within the tumour. To complete an electrical circuit grounding pads attached to the patient's thighs function as neutral electrodes. An alternating current between these electrodes, which flows through the body of the patient, induces conductive heating around the active electrode with temperatures 50–100 °C leading to tumour cell death and thermal coagulation necrosis. Besides possible skin burns and collateral damage by uncontrolled electrical current pads, the most important limitation of this technique is the poor local effectiveness in large size tumours [7], [8], [9], [10]. Although electrodes such as expandable electrodes, multi-probe arrays (cluster electrode) and cooled-tip electrodes (to avoid carbonization around the electrode) have shown to increase the sizes of the ablation zone, many overlapping ablations are often necessary for tumour sizes ≥3.5 cm especially if you want tumour free margins of at least 1 cm to be ablated [11], [12], [13], [14], [15], [16]. Furthermore, it is very difficult and often even impossible to determine regions of remaining vital tumour tissue which need to be treated with overlapping ablations, on either ultrasound or CT directly after the first ablation.

Novel “bipolar” radiofrequency systems in which both electrodes are located on one application instrument separated by an insulator have been recently developed to overcome these problems of monopolar RFA, and have already demonstrated their safety and effectiveness in experimental studies [17], [18]. A multipolar RFA concept which allows up to three radiofrequency probes to be placed simultaneously within the tumour has also shown to be feasible [19], [20], [21].

The aim of the present study was to demonstrate the first experiences with a new bipolar expandable system in which two separate electrodes are placed not within the tumour tissue but marginal to the tumour, plan-parallel and opposed to each other (InCircle™, RFA Medical Inc., Fremont, USA) and to evaluate safety, feasibility and effectiveness.

Section snippets

Patient selection

Between November 2007 and November 2008 eight consecutive patients with 11 large size liver malignancies were considered suitable for treatment with the bipolar RFA system (InCircle, RFA Medical Inc., Fremont, USA) (Table 1): 9 colorectal liver metastases (CRLM), 1 large size carcinoid liver metastasis and 1 hepatocellular carcinoma (HCC) ≥3.5 cm. Inclusion criteria for performing bipolar RFA were (1) tumour diameter 3.5–8 cm; (2) no evidence of extra-hepatic metastases; (3) complete ablation of

Technical results

In all patients the bipolar RF ablation was considered technically successful based upon the primary and final endpoints (Table 1). Average ablation time was 16 min (range 8–29 min). The power at time of primary roll-off was 135 W in all cases and 118 W on average for the secondary roll-off (range 100–135 W). In 5/11 tumours the electrodes were re-positioned once and in 2/11 tumours the electrodes were re-positioned twice before reaching an adequate hyperechoic and non-enhancing ablation zone. In

Discussion

The first available single needle monopolar electrodes generated cylindrical shape coagulation volumes with a diameter of only 1.6 cm [24]. To create larger volumes of coagulation necrosis several systems were developed, many of which are now commercially available. The most well known systems nowadays use expandable electrodes and/or internal applicator cooling or perfusion electrodes. Expandable monopolar RF applicators featuring an umbrella-shaped array generates more spherical-shaped tumours

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