Objective: To determine whether alternative radiofrequency (RF) application with dual probes has advantages over sequential or simultaneous RF application for creating larger coagulation necrosis.
Materials and methods: Using 2 17-gauge internally cooled electrodes and a 200-watt generator (CC-3 model, Radionics), RF energy was applied sequentially (group A, n = 20), simultaneously (group B, n = 20), or alternately (group C, n = 20) to explanted bovine liver. After preliminary experiments with a probe distance of 2-5 cm, a distance of 2 cm and 3 cm were chosen for main experiments. Total duration of the RF application was 10 minutes. In the alternative mode, the energy was applied alternately to both RF electrodes in 2-second intervals. Changes occurring in tissue impedance, current, power output, and temperature at the midpoint between the 2 electrodes were measured. The technical parameters, temperatures, and dimension of the ablated area were compared in the 3 groups using analysis of variance or Kruskal-Wallis test.
Results: In the groups B and C, the impedance was gradually decreased during RF application and the mean current flow of both groups was 1550 +/- 130 mA and 1375 +/- 175 mA, respectively. However, in the group A, the impedance was markedly increased during RF application, and the mean current was 940 +/- 484 mA (P < 0.05, between groups A and B, and groups A and C). With 3-cm spacing, the alternative RF application created oval-shaped ablation zones with larger shortest axis diameter at the midpoint than either the sequential or simultaneous RF application: 12.0 +/- 7.1 mm in group A; 27.0 +/- 3.1 mm in group B; 34.9 +/- 3.4 mm in group C (P < 0.05). With 2 cm spacing, the corresponding figures were 25.3 +/- 7.8 mm in group A; 34.9 +/- 7.8 mm in group B; 41.5 +/- 1.8 mm in group C (P < 0.05): the differences between groups A and B, and between groups A and C were statistically significant (P < 0.05). With 3-cm spacing, the temperature at the midpoint between the 2 probes was higher in group C (102 degrees C) than in either the group A (62 degrees C) or the group B (78 degrees C; P < 0.05). With 2-cm spacing, groups B and C showed higher temperature than group A (P < 0.05), but the difference between groups B and C was not significant (P > 0.05).
Conclusion: The alternative RF application creates larger, more regular ablation zones than either the sequential or simultaneous RF application. This result suggests that use of an alternating RF power application will improve the results of RF ablation for the treatment of larger tumors.