Radiofrequency ablation of pulmonary tumors and normal lung tissue in swine and rabbits

Objective: The purpose of the present study was to examine the following during radiofrequency ablation (RFA): (1) the risk of hemorrhage from intrapulmonary large vessels; (2) the risk of incomplete ablation of pulmonary tumors; and (3) the late effect on lung tissue. Materials and methods: A 17-gauge, cool-tip-type radiofrequency electrode was used. The damage to the vessels and bronchi was examined by the injection of a colored silicone rubber, a liquid compound that hardens after injection. To examine the risk of hemorrhage from intrapulmonary large vessels, RFA was conducted at eight sites near the central pulmonary vessels in two swine. To examine the risk of an incomplete ablation for pulmonary tumors, 10 pulmonary nodules were made from a gelatin mixture in another two swine and were treated by RFA. To examine the late effect on lung tissue, RFA was conducted on the peripheral lung in 10 rabbits, and then the ablated regions were examined on days 1, 7, 14, 21, and 28 after RFA. Results: The use of colored silicone rubber enabled us to examine the intrapulmonary vessels and bronchi for opening and leakage. RFA did not damage the large intrapulmonary vessels, even when they were: located within the ablated regions. Lung tissue surrounding the gelatin nodules was hardly ablated over its entire circumference. Six of 10 gelatin nodules (60%) showed nonablated areas on the peripheral edges of the nodules. From 21 days after RFA, the ablated rabbit lung formed noninfectious cavities by communicating with the surrounding bronchi. Conclusion: It was improbable for hemorrhage to occur even when RFA was conducted near the large intrapulmonary large vessels. Because an incomplete ablation that left tumor cells at the site of ablation could occur during surgery due to the difficulty of ablating the entire tumor circumference, CT scan-guided RFA would be preferable to a surgical approach for making a safe margin. Cavity formation can occur beginning 21 days after RFA, which should be carefully followed up in a clinical setting to identify infection, especially in immunocompromised patients.