Dielectric properties, thermal properties, blood perfusion rate: which biophysical parameter is the leading source of variability of microwave ablation models in lung?

BACKGROUND The large variability in outcomes following microwave ablation (MWA) of pulmonary tumors highlights a need for quantitative methods to assess 3D temperature profiles accounting for tissue-specific biophysical characteristics. The goal of this study is to identify the least and most influential biophysical parameters on the ablation zone.

METHODS A computational bioheat transfer model was built to simulate a 2.45 GHz microwave applicator positioned within a 2 cm diameter tumor. Simulations were conducted using 60 W - 10 min energy settings and considering low and high values of: 1) relative permittivity, 28.3-50.4 and effective conductivity, 1.0-1.9 (Sm-1); 2) volumetric heat capacity, 1.3-3.5 (MJm-3K-1) and thermal conductivity 0.2-0.4 (Wm-1K-1); 3) blood perfusion rate of tumor periphery-parenchyma, 5-9 (kgm-3s-1). Length (L60) and diameter (D60) of the 60 °C isotherm, volumetric thermal coverage of the tumor without (TM0) and with 5 mm margin (TM5) were quantified.

RESULTS The variabilities in the volumetric heat capacity and blood perfusion rate at the tumor-lung parenchyma boundary yield differences between 5.7 - 11.4% (TM5), 3.1-4.6 mm (D60), 3.0-4.4 mm (L60). Variabilities in baseline values of dielectric properties yield 3% (TM5) and 1.2 mm (D60 and L60) differences.

CONCLUSION Thermal properties and blood perfusion between tumor and surrounding tissue are the most impactful parameters on achieving adequate treatment margin following lung MWA. This quantitative analysis provides insight on the tissue biophysical properties that warrant deeper experimental assessment in order to inform treatment planning of lung MWA.