Physical modeling of microwave ablation zone clinical margin variance

Area of Science:

• Medical Physics
• Biomedical Engineering
• Interventional Radiology

Background:

• Microwave ablation (MWA) is a minimally invasive treatment for liver tumors.
• Accurate modeling of MWA is crucial for effective treatment planning.
• Understanding the influence of tissue heterogeneity and surrounding anatomy is key to improving MWA outcomes.

Purpose of the Study:

• To simulate and quantify the impact of biophysical parameter heterogeneity (tumor vs. healthy tissue), applicator placement, and proximity to large blood vessels on MWA treatment effect area.
• To identify critical biophysical properties influencing MWA treatment outcomes for improved clinical modeling.

Main Methods:

• Developed two-compartment computational models simulating MWA in the liver using a 915 MHz applicator.
• Incorporated variable dielectric and thermal properties for healthy (normal, fatty, cirrhotic) and malignant liver tissues based on literature data.
• Simulated variations in antenna position (±5 mm) and the presence of blood vessel heat sinks of varying sizes and distances.

Main Results:

• Tissue property variations (e.g., fatty liver, cirrhosis) caused up to a 36% increase in ablation volume.
• Antenna placement shifts of 5 mm resulted in minimal changes (<1.5 mm) to absolute ablation zone size but caused significant margin discrepancies (approx. 6 mm).
• Proximity to blood vessels reduced ablation margin by up to 11% (Dice coefficient), highlighting their heat sink effect.

Conclusions:

• Malignant and healthy liver tissues can be approximated as having similar dielectric properties for MWA modeling.
• While antenna placement minimally affects ablation zone size, it critically impacts the achieved treatment margins.
• The cooling effect of nearby blood vessels is a significant factor requiring consideration in MWA treatment planning.