RF Ablation

All ablation procedures were performed under intravenous sedation with 100 mg of phentanyl citrate and local anesthesia with 1% lidocaine. Internally cooled electrodes with impedance-controlled pulse current from a 200 W generator (Radionics, Burlington, MA, USA) were used for ablation (Fig. 1). All tumors were treated with a single (1- or 2-cm active tip) needle electrode. We usually started with RF energy of 20 W and then gradually increased the energy by 10W every 2min. When the impedance of the tumor reached 20W larger than that at the beginning of ablation (the so-called breakdown) and the temperature of the tumor exceeded 60°C, we completed the ablation.

All procedures were performed with CT fluoroscopic guidance in an Interventional CT System Suite in our hospital (Figs. 2 and 3b). On the basis of the size and location of the lesion on CT scans, overlapping ablations were performed by repositioning the needle to ablate the entire tumor. In almost all cases,

Fig. 1. An internally cooled electrode (a) with impedance-controlled pulse current from a 200-W generator (b) was used in ablation. We usually use an electrode with a 15-cm shaft length and a 1- or 2-cm active tip. The diameter of the electrode is 17 gauge

Fig. 1. An internally cooled electrode (a) with impedance-controlled pulse current from a 200-W generator (b) was used in ablation. We usually use an electrode with a 15-cm shaft length and a 1- or 2-cm active tip. The diameter of the electrode is 17 gauge

Fig. 2. Interventional computed tomographic (CT) suite provides CT fluoroscopy. An operator inserts an electrode under CT fluoroscopic guidance into the renal lesion. This suite also provides angiography equipment

Fig. 3. A 60-year-old man with left renal-cell carcinoma (RCC). He had a right nephrec-tomy 3 years previously because of RCC. The contrast-enhanced CT scan shows an exo-phytic renal tumor 3cm in diameter (a). Radiofrequency (RF) ablation with the use of an internally cooled electrode under CT fluoroscopic guidance was performed with the patient in the prone position (b). The 1-year follow-up CT scan shows complete disappearance of enhancement of the tumor (c)

Fig. 3. A 60-year-old man with left renal-cell carcinoma (RCC). He had a right nephrec-tomy 3 years previously because of RCC. The contrast-enhanced CT scan shows an exo-phytic renal tumor 3cm in diameter (a). Radiofrequency (RF) ablation with the use of an internally cooled electrode under CT fluoroscopic guidance was performed with the patient in the prone position (b). The 1-year follow-up CT scan shows complete disappearance of enhancement of the tumor (c)

the electrode was initially placed to enable ablation of the portion of the tumor neighboring on normal renal parenchyma. Ablation of this initial placement was thought to induce larger burn diameters by obstructing the cooling effect of the blood flow from the adjacent normal parenchyma. We usually repositioned a needle within 1 cm from the track of the needle positioned immediately before. If the axis of the tumor parallel to the electrode was longer than the expected burn length, overlap was obtained by pulling the electrode back for the appropriate distance and performing another ablation. At the end of the ablation procedure, dynamic CT scans of the treated kidney were performed in the Interventional CT System Suite to confirm the disappearance of enhancement of renal tumors by contrast material. If residual enhancement was observed in the tumor, further ablations were performed until the enhancement disappeared completely.

Fig. 2. Interventional computed tomographic (CT) suite provides CT fluoroscopy. An operator inserts an electrode under CT fluoroscopic guidance into the renal lesion. This suite also provides angiography equipment

In one patient whose RCC was incidentally discovered during a survey for metastatic lesions of esophageal carcinoma, transcatheter arterial chemo-embolization of RCC was performed before the start of radiotherapy and chemotherapy of the esophageal carcinoma. After completion of 3 months of radiotherapy and chemotherapy, RF ablation of the embolized RCC was performed. The diameter of the tumor was 33 mm at the time of RF ablation; it had been 40 mm before embolization.

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