Effect of changes in lung physical properties on microwave ablation zone during respiration.

Microwave ablation is a promising minimally invasive treatment for cancer. However, due to the respiratory movement of the lungs, it is very difficult to accurately predict and control the microwave ablation zone. Therefore, the influence of the changes of the physical parameters of the respiratory process on the microwave ablation zone is studied. Firstly, based on the 4D-CT describing the respiratory process of the lungs, all the image data are from 100 non-small cell lung cancer radiotherapy patients (50 males and 50 females, average 58 years, range 55-61 years). According to the theory of porous media, the change of the effective thermal conductivity of the lung tissue during the breathing process is obtained. The effective thermal conductivity of the lung parenchyma during respiration varies from 0.16 to 0.20 W/m °C, with the lowest vale at the end of inspiration and the highest at the end of expiration. The transient problems during microwave ablation of pulmonary tissue are analyzed by finite element method. The changes of relative permittivity, conductivity and density changes during the breathing process are also considered. The results show that the microwave ablation zone is significantly larger under dynamic physical parameters. At the end of expiration, when the tissue parameter is set to constant, the ablation lesion area is more concentrated around the tip and slot of the antenna, and the backward heating effect is smaller, Ablation volume was superior in nonventilated lungs. Therefore, single-lung ventilation can be considered during pulmonary ablation to reduce the impact of breathing on the ablation area. These findings can be useful to further our understanding the MWA and hold promise towards achieving successful treatment objective as well as enhanced therapeutic output via improved treatment planning and strategy. This study provides the basis for clinical pulmonary ablation and can also be used as a preoperative plan to provide guidance to physicians. © Korean Society of Medical and Biological Engineering 2020.