Microwave ablation of lung tissue: impact of single-lung ventilation on ablation size

Thermal ablation is increasingly used to treat pulmonary tumors in medically inoperable patients. Most procedures are performed with sedation in the radiology suite. Ideally, the ablation should encompass the entire tumor volume with a surrounding margin of necrosis; however, ablation may not be as effective in the normal aerated lung surrounding a denser tumor. Inducing atelectasis of the lung may potentially increase ablation volumes and increase local cancer control. This study examines the effect of single-lung ventilation on ablation size using a microwave system.

Twenty microwave ablation procedures were performed in the lungs of 10 swine. Bilateral thoracotomy using a clamshell approach was used. In one lung, ablation was performed with continuous ventilation. In the contralateral lung, single-lung ventilation was achieved by clamping the bronchus before ablation. The ablated lobes were resected and sent for pathologic analysis. Routine and supravital staining was performed.

The ablation zone was clearly demarcated on gross examination, and in all cases 100% ablation occurred, without skip areas of viability. The ablation zones were elliptical with the long axis parallel to the axis of the ablation probes (active tip, 3.7 cm). Ablation diameters and volume were compared between the ventilated and nonventilated lungs. Ablation volume was superior in nonventilated lungs (10.74 cm(3) versus 7.35 cm(3); p = 0.039) primarily because of differences in the short axis of the ablation zone.

Microwave energy can effectively ablate normal pulmonary parenchyma without skip areas of viable tissue within the gross ablation field. The volume of necrosis is increased in nonventilated lungs, suggesting that ablation results can be improved in patients by using general anesthesia with single-lung ventilation. Future studies will be required to confirm this hypothesis.