Numerical simulation study on the thermo-mechanical coupling damage mechanism in microwave ablation of lung tumors

Lung cancer is one of the most threatening malignant tumors globally, and microwave ablation (MWA) serves as a crucial minimally invasive approach for treating early-stage patients who are intolerant to surgery. However, the lung, as a typical porous medium, remains unclear in terms of the correlation mechanism between thermal stress evolution during MWA and postoperative complications such as cavities. This study aims to reveal the thermo-mechanical coupling damage mechanism during lung MWA through numerical simulation. Based on the porous medium theory and the two-phase lag heat transfer model, an electromagnetic-thermal-mechanical multiphysics coupled finite element model was constructed to simulate the complete ablation process of lung tumors using a 2450 MHz microwave antenna. The simulation results indicate the presence of two damage risk zones with distinct mechanical characteristics during MWA: the high-temperature core zone, which is dominated by thermal coagulation necrosis and phase change contraction, bears the highest equivalent stress; whereas the tissue transition zone, due to significant gradients in temperature and material properties, becomes a region where strain first increases and then decreases, accompanied by shear stress concentration, making it a high-risk area for tearing-type damage and potential cavity formation. During the cooling phase, significant redistribution and relaxation of stress occur in both the core and transition zones. The presence of residual strain and stress confirms that irreversible phase change damage is the primary mechanism responsible for the permanent volume reduction of the ablation zone. This study systematically elucidates the "dual risk zone" mechanism of thermo-mechanical coupling damage in lung MWA, reveals the importance of mechanical evolution during the cooling phase, and provides an important theoretical basis for developing precise and safe ablation strategies based on mechanical thresholds.