Cool tip

Treatment strategies in our institution are based on the Japanese guidelines [11 (link)]. First, we investigated whether definitive treatment can be accomplished by surgical resection or whether RFA is an alternative to surgical resection. RFA was performed as described previously [12 (link)]. Briefly, the procedures were performed under real-time ultrasound guidance (Power Vision 8000, Aplio XV, Aplio XG, or Aplio 500; Toshiba, Tokyo, Japan) and a 17-gauge cooled-tip electrode (Cool-Tip; RF Ablation System, Covidien, Boulder, Colombia, CO). Under conscious sedation, an electrode was inserted and radiofrequency was delivered for 6–15 min for each lesion. As appropriate, intrapleural or intraperitoneal fluid infusion was performed before electrode insertion. We evaluated effectiveness via dynamic CT or MRI on the day after RFA. The treatment assessments were performed as published previously [12 (link)]. To judge if ablation was complete or not, we compared images taken before and after ablation. The definition of completely ablated was as follows: post-ablation CT or MRI indicated a non-enhanced area covering the lesion where the tumor was located prior to ablation, outlined with a safety margin in the surrounding liver parenchyma.

The device used has been described in detailed in a previous report.²⁶ Before ablation, a 2‐cm skin incision was made using a scalpel, and 1% lidocaine (Yi you, Beijing, China) was subcutaneously injected as local anesthesia to moderately sedate each patient. An 18‐gauge cutting needle in an automatic biopsy gun was used to carry out the biopsy before thermal ablation. Consequently, an internally cooled, 17‐gauge, 15 cm, electrode, with a 2‐ or 3‐cm long exposed metallic tip (Cool‐tip; Covidien) or a 15‐gauge antenna (KY‐2000, Kangyou Medical) was percutaneously inserted into the tumor as preoperatively planned using US or CT guidance. The RF energy was delivered for 12‐16 minutes at impedance control mode, while for MWA, a power output of 50 W for 10 minutes was routinely used. The electrode or antenna was inserted repeatedly after minor changes were made to the tip angle, in order for the ablation zone to completely cover the tumor area with a safety margin of >0.5 cm. Finally, the MWA or RFA needle tract was cauterized during needle withdrawal.

Our RFA procedures were percutaneously performed by 1 of 3 radiologists who had 13, 11, and 9 years of clinical experience, respectively. RFA procedures and data assessment were based on Detailed methods of RFA are described in previous studies.^{[9 (link),10 (link)]} All patients were treated when they were under IV conscious analgesic sedation. Commercially available internally cooled electrode systems with generators (Cool-tip RF System, Covidien, Mansfield, MA, USA; VIVA RFA System, STARmed, Goyang, Korea) were performed for all patients with HCCs in our cohort. Various electrodes including the single electrode with a 2 cm active tip, or with an adjustable active tip (Proteus RF Electrode, STARmed), or a cluster-electrode (Cool-tip, Covidien; Octopus, STARmed) were used according to tumor size and equipment availability. The energy deposition algorithm used was consistent with the introduced protocols. Our strategy was to include an ablative margin of at least 0.5 cm of normal hepatic parenchyma surrounding the tumor, as well as the entire tumor itself, with the exception of the perivascular portions and subcapsular. Our strategy of RFA was finished when the hyperechoic ablation range was large enough to cover the entire tumor and the expected ablative margin.

Our ultrasound-guided percutaneous RFA technique has been previously described in detail.^{10 (link)} In brief, tumor ablation was performed by 1 of 3 interventional radiologists with >5 years of experience in a blind manner. We used single electrodes with an internally cooled tip (Cool-tip™; Covidien, Burlington, MA), cooled wet tip (Jet-tip^®, RF Medical Co., Ltd., Seoul, Korea), and multitined expandable tip (Proteus^®, STARmed Co., Ltd., Goyang, Korea), as appropriate. The RFA current was elevated 20 W/min starting from 60 W with internally cooled tip and multitined expandable tip, or 30 W/min starting from 50 W with wet tip using the automatic impedance control method and 200-W generator (Mygen M-2004 Radiofrequency System; RF Medical Co.) for 8 to 18 minutes.