Hepatic bipolar radio-frequency ablation between separated multiprong electrodes

Radio-frequency (RF) ablation has become an important means of treatment of nonresectable primary and metastatic liver tumors. Major limitations are s mall lesion size, which make multiple applications necessary, and incomplet e killing of tumor cells, resulting in high recurrence rates. We examined a new bipolar RF ablation method incorporating two probes with hooked electr odes (RITA model 30). We performed monopolar and bipolar in vivo experiment s on three pigs. The electrodes were 2.5 cm apart and rotated 45 degrees re lative to each other. We used temperature-controlled mode at 95 degreesC. L esion volumes were 3.9 +/- 1.8 cm(3) (n = 7) for the monopolar case and 12. 2 +/- 13 cm(3) (n = 10) for the bipolar case. We generated finite-element m odels (FEMs) of monopolar and bipolar configurations. We analyzed the distr ibution of temperature and electric field of the finite element model. The lesion volumes for the FEM are 7.95 cm(3) for the monopolar and 18.79 cm(3) for the bipolar case. The new bipolar method creates larger lesions and is less dependent on local inhomogenities in liver tissue-such as blood perfu sion-compared with monopolar RF ablation. A limitation of the new method is that the power dissipation of the two probes cannot be controlled independ ently in response to different conditions in the vicinity of each probe. Th is may result in nonuniform lesions and decreased lesion size.