Investigation of perfusion effect in bio-heat transfer during thermal surgery and thermotherapies
Cancer is one of the leading causes of death in the United States. Treatment modalities such as chemo or radiation therapy can severely affect patient's quality of life. Patient-specific minimally invasive therapies, on the other hand, can provide targeted treatment with a promise to maintain quality of life with less recovery time. Radio-Frequency (RF) and laser induced thermal therapies are among those targeted therapies that are used in clinics but still need scientific studies. The key to the success of any thermotherapy is the prediction and control of temperature distribution in both cancerous and healthy tissue regions, given that these regions are identifiable. One of the challenges in predicting the temperature field accurately is when differently sizes of blood vessels are entangled in or are located nearby the tumors, which could cause significant heat loss. It was reported that any vessel with a size larger than 60 mum in diameter prescribes thermally significant behavior. However, a rigorous study is needed to quantify the effect of vessel structure in the context of thermal therapies to ensure accurate treatment planning and thermal dosage delivery. In this study, heat transfer in biological tissue is investigated by numerical methods to predict temperature distribution in RF ablation. The governing equations involve the coupling of two scalar fields such as voltage and temperature. To evaluate the tissue damage, the solution of the bio-heat equation solved by the finite element simulations are used to characterize the intensity of the temperature field, which was transformed to damage index. The perfusion effect is studied for cases of different vessel sizes and distances between a vessel and RF probe and are evaluated numerically. In addition, the perfusion effect in thermo-therapies applied after knee surgery is investigated and compared with experimental results. Good agreements are obtained.