Hepatocellular carcinoma (HCC), commonly known as the liver cancer, is a severe health concern worldwide. For patients with liver tumors that are difficult to remove through traditional treatments such as radiation, chemotherapy and partial hepatectomy, there is the option of radiofrequency ablation (RFA) treatment. RFA is a minimally invasive procedure that is currently treating liver tumors that are relatively small in size. Radiofrequency ablation uses currents to heat up the tissue of the tumor. Once the temperature of the tissue reaches approximately 60° C tissue necrosis begins to occur . With current RFA probes, ablation lesions are typically 3–5.5 cm in diameter . It is important that all of the tumor tissue is ablated, so it is necessary to also kill a small amount of the surrounding healthy tissue. At least 1 cm of healthy tissue should be ablated to ensure the tumor will not recur . Hence, many studies [3, 4] have attempted to increase the RFA ablation zone through various methods including adding saline to the tissue, predicting the optimal power level, etc.
To focus on safely increasing the size of the ablation zone and to improve upon the spherical geometry of the tumors, the “Christmas tree” and “umbrella” style probes , which utilize multi-pronged electrodes (tines), are currently available in the market. The electrodes, or wires of the probe, are responsible for producing heat and making contact with the liver tissue at all time in order to execute the tissue ablation. For the umbrella and Christmas tree style probes, the drawbacks include: 1. the gauge of the tines limit the ablation scope of the probes; 2. their ability to achieve higher volumes of cell death are limited due to their static geometry, which has fixed diameters; 3. towards the outer edge of the tumor, due to their static geometry and the loss of contact with live tissues, the rate of killing cancerous cells decreases drastically due to the decrease in heat transfer rate, which is a result of the lack of heat sink from perfusion in the live tissues .
It was noticed that an improvement could be made to the efficiency of these multi-pronged electrodes if they were free to expand as the area of tissue was ablated. Therefore, a novel dynamic RFA probe was proposed by Lau and Han and numerical simulations using COMSOL Multiphysics Joule heating module have concluded that this dynamic RFA probe can achieve a higher ablation volume with a shorter procedure time . The main goal of this study is to realize the design of this dynamic RFA probe with expandable electrodes to create the largest and most replicable ablation zone. In this study, the deployment mechanism and the proposed design of the dynamic probe are discussed and the analytical solutions of the electrode expansion profiles are presented. The ablation zones are estimated analytically based on the dynamic expansion of the electrodes.