Optimizing Microwave Ablation for Lung Nodules: Impact of Power and Application Strategy on Treatment Zone Size

Purpose: The use of minimally invasive options such as microwave ablation (MWA) zones in the lung depends on energy delivery dynamics and tissue-air interactions. This study investigates how modulation of power and ablation timing alters ablation zone (AZ) volumes, providing insight into the physics of thermal conduction and energy deposition in the lung's aerated and vascular tissue. Evaluation of how continuous versus intermittent ablation protocols influence AZ formation could thus have implications for optimizing treatment outcomes in treating primary and metastatic lung nodules.

Materials and Methods: MWA probes were placed into swine lungs under fluoroscopic guidance. Protocols involved continuous or intermittent ablations performed for 8, 4, 2, or 1 minutes, with total ablation times of 8 or 4 minutes, at either 65 or 30 watts. AZ volumes were assessed ex vivo.

Results: Intermittent MWA significantly reduced AZ size compared with continuous ablation. At 65 watts, applying 2- or 1-minute intervals reduced AZ volume by 28% and 60%, respectively (Continuous: 3.07 cm³ ± 0.27 vs. 2 minutes: 2.22 cm³ ± 0.30, p=0.0159; 1 minute: 1.24 cm³ ± 0.18, p< 0.001). At 30 watts, AZ volumes were reduced by 25% and 53% (Continuous: 1.50 cm³ ± 0.40 vs. 2 minutes: 1.12 cm³ ± 0.21, p=0.013; 1 minute: 0.81 cm³ ± 0.15, p< 0.002). Reducing power by 53% led to a 51% decrease in AZ volume, and this gap widened with longer ablation duration, reaching a 60% reduction at 8 minutes. This likely reflects the tissue charring and heat loss in aerated lung parenchyma that limit further zone expansion at lower power.

Conclusion: Continuous high-power MWA produces significantly larger ablation zones in lung tissue compared to intermittent or low-power protocols. The linear efficiency gap between high- and low-power ablation further widens with longer duration, likely due to tissue desiccation and heat dissipation unique to the lung. These findings emphasize careful selection of initial power and delivery strategies to achieve adequate margins and minimize undertreatment risk in lung tumor ablation and may provide a foundation for optimizing ablation algorithms and developing next-generation energy-delivery devices.

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