Technical characterization of a new bipolar and multipolar radiofrequency device for minimally invasive treatment of renal tumours

To investigate the technical characteristics of a newly developed device for bipolar and multipolar radiofrequency ablation (RFA) of kidney tissue with a resistance-controlled power output. The standardized model of the isolated perfused ex vivo porcine kidney was used. Two different applicators (20 and 30 mm active length) were selected for bipolar RFA, and one pair of applicators (2 x 30 mm active length) for multipolar RFA. RF energy was applied at different power levels (20, 30, 60 W) depending on the total active length of the electrodes. Treatment times were 1, 3, 5 and 9 min. The ablation cycles were recorded in continuous digital real-time and displayed on a monitor showing pre-set power, actual applied power, applied energy, tissue resistance, and impedance. Lesion sizes were measured macroscopically. A coagulation coefficient (coagulated tissue volume per applied energy unit) was calculated. There was a dosage-effect relationship between the generator power/treatment time and the sizes of the lesions. With increasing treatment time, less tissue volume was coagulated per unit of applied energy. The actual applied energy was lower than that calculated theoretically. The resistance and impedance values for the 30-W applicator were lower than those of the 20-W applicator. The technical features of this RFA device, with internally cooled bipolar and multipolar applicators and a resistance-controlled power output, represents an innovative improvement in RF technology. In vivo studies are needed to confirm the expected advantages and the suitability of this device for complete and reliable ablation of renal tumours.