Large-volume tissue ablation with radio frequency by using a clustered, internally cooled electrode technique: Laboratory and clinical experience in liver metastases

PURPOSE: To evaluate whether coagulation necrosis achievable with radio- frequency (RF) ablation can be increased by using a cluster of closely spaced electrodes. MATERIALS AND METHODS: RF was applied to ex vivo liver (n = 68), in vivo liver (n = 12), and in vivo muscle (n = 15) by using a cluster array of three separate internally cooled electrodes spaced 0.5 cm apart. The diameter of coagulation necrosis achieved with optimal RF deposition (1,400- 2,150 peak mA) for 5-60 minutes of RF application was determined for electrode tip lengths of 1.5-3.0 cm and compared with that obtained by using a single electrode and otherwise similar technique. Ten patients with solitary intrahepatic colorectal metastases were also treated by using cluster electrode RF ablation. RESULTS: In ex vivo liver, simultaneous RF application to electrode clusters for 15, 30, and 45 minutes produced 4.7 cm ± 0.1, 6.2 cm ± 0.1, and 7.0 cm ± 0.2 of coagulation necrosis, respectively. In in vivo liver and muscle, RF applied to electrode clusters for 12 minutes yielded 3.1 cm ± 0.2 and 7.6 cm ± 0.4 of coagulation, respectively. RF application to a single electrode produced maximal coagulation of 2.9 cm in ex vivo liver, 1.8 cm in in vivo liver, and 4.3 cm in muscle (P <.01, all tissues). In colorectal metastases, a single 12-15- minute application of RF to an electrode cluster induced 4.5-7.0 cm of coagulation necrosis. CONCLUSION: Simultaneous RF application to a cluster of three closely spaced internally cooled electrodes enables a larger volume of coagulation in ex vivo liver, in vivo tissues, and hepatic colorectal metastases than previously reported.