The purpose of this study was to compare the shape and volume of the radio-frequency induced lesions produced by two commercially available radio-frequency ablation (RFA) systems, the expandable and cooled-tip needles, in clinical patients and an experimental model.

A twelve-array anchor expandable needle electrode and a single cooled-tip needle electrode were used to treat hepatic tumors with a single session in 23 patients (20 hepatocellular carcinomas and 3 hepatic metastases) and fourteen patients (10 hepatocellular carcinomas and 4 hepatic metastases), respectively. Twenty RFA induced lesions were created with each system in 10 explanted bovine livers. The shape of the RFA induced lesions were divided into oval lesions along or perpendicular to the axis of the electrode and spherical lesions, and we then calculated the volumes of the RFA induced lesions.

Fourteen (61%) lesions of the 23 patients treated with the expandable system were oval perpendicular to the axis of the electrode and nine (39%) of the lesions were spherical. All the lesions (100%) of the 14 patients treated with the cooled-tip needle were oval along the axis of the electrode. In the ex vivo bovine livers, the shape of the all RFA induced lesions was oval perpendicular to the axis of the electrode for the expandable needle, and oval along the axis of the electrode for the cooled-tip needle. The mean diameter and volume of the RFA induced lesions in the patients were 3.35±0.56cm and 19.9±6.53 cm³, respectively, for the expandable needle and 3.58±0.78 cm and 23.19±5.27 cm³, respectively, for the cooled-tip needle. In the ex vivo model, the mean diameter and volume of RFA induced lesions were 3.41±0.59 cm and 26.59±8.02 cm³, respectively, for the expandable needle, and 4.04±0.65 cm and 33.82±6.16 cm³, respectively, for the cooled-tip needle (p<0.05).

These results indicate that the shape of RFA induced lesions with the expandable needle were oval perpendicular to the axis of the electrode but those with the cooled-tip needle were oval along the axis of the electrode in both the clinical and experimental models. The cooled-tip needle induced significantly larger lesions than the expandable needle in the clinical patients and the experimental model. We need to consider these characteristic findings for RFA when we are performing such procedures.