Radio-frequency (RF) ablation is one of the most widely used methods for the treatment of hepatic malignancies. A finite element method (FEM) analysis was employed to determine the thermal dose delivered to the tumor/tissue region. We simulated heating within a RF probe implanted in generic tumor surrounded by healthy tissue using ANSYS. The 3-D model consists of a tumor / tissue region into which the RF probe is embedded inside the tumor. One-quarter symmetry was then invoked. The blood flow was modeled using Penne’s bio-heat transfer equation with differing perfusion rates between the healthy tissue and tumor volume based on literature values. The resulting temperature distribution throughout the region was determined over time. A program was written in Visual Basic to extract the temperature distribution data in the tumor/tissue region and calculate the thermal dose throughout the region. This was done by using a time–temperature Arrhenius relationship for chemical and physical rate process. Tissue necrosis is assumed complete when a thermal dose of one hour has been achieved at 43 °C. In the present study, the geometry of the electrode had a significant effect on the size of the volume of necrosis. It was found that the lower portion of the tumor did not receive the specified thermal dose relative to the upper portion of the tumor in single setting during the RF ablation therapy. This might be due to the Ni-Ti electrode, which protruded only from the top surface of the trocar. The effectiveness of the existing probe can be improved by having one more set of electrodes protruding out from the lower curved surface of the trocar. It was found that the modified probe significantly improved heating in the lower portion of tumor/tissue area, providing more symmetry between the upper and lower portion.
Absorption efficiency of gold nanorods determined by quantum dot fluorescence thermometry
