Radio Frequency Thermal Treatment of Liver Tumours : -Influence of Blood Perfusion and Large Vessels

Abstract: Radio frequency ablation (RFA) is a commonly used minimally invasive method of treating liver cancer tumours which utilises RF current for heating tumour tissue up to a lethal temperature. RF current is generated by a power generator and applied to the tumour by an electrode which is inserted into the tumour either during percutaneous or open surgery. RFA is a method that has great advantages compared to traditional surgical resection of tumours due to minimal invasiveness, it can be used for a greater number of patients and enables repeated treatments. Even though there are many advantages coupled to RFA there are still some problems and difficulties associated with the method. One of these problems is the cooling effect from large vessel blood flow within the liver, the so called heat sink effect. The aim of this master thesis work has been to develop a theoretical finite element model of RFA within Comsol Multiphysics software. This theoretical model has been used to simulate blood perfusion effects on resulting ablation volume. The effects from different large vessel blood flow parameters has been investigated, these parameters are: blood flow velocity, blood vessel diameter and distance between blood vessel and RF electrode. A factorial design has been utilised to setup parameter levels for the different simulations. A linear- and a second degree regression model has been calculated based on simulation results. The parameter with largest impact on simulative ablation volume and the interaction effects between the parameters were determined from the regression model coefficients. In addition to this has two simulations been performed, modelling perfused- and unperfused liver tissue, in order to investigate the effects resulting from microvascular perfusion. The result shows that the parameter with largest impact on simulative ablation volume are the distance, it was also shown that there are a small interactional effects between diameter and distance, where a small distance increases the effect from a varying diameter. Modelled microvascular perfusion was shown to give a decrease in simulative ablation volume. A shortage of this master thesis work is the lack of experimental verification of the developed model.