Thermal dose versus isotherm as lesion boundary estimator for cardiac and hepatic radio-frequency ablation

Radio-frequency (RF) ablation is a therapy that destroys pathologic tissue by heat. Cardiac ablation is a widely used treatment method for a number of cardiac arrhythmias. Hepatic ablation is becoming an increasingly popular for treatment of liver tumors. Mathematical ablation models have been developed to predict dimensions of inflicted tissue damage (i.e. RF lesion). In most models the 50 °C isotherm has been used to determine boundary between viable and dead tissue. It is well known that accurate damage prediction has to take the temperature history (i.e. thermal dose) into account. We implemented the widely used Arrhenius damage model into our finite element method computer models of cardiac and hepatic RF ablation. We simulated cardiac ablation for 45 s, and hepatic ablation for 12 min. We compared the lesion boundary determined by the damage model to the 50 °C isotherm. For the cardiac model, the isotherm overestimated the lesion diameter by 4.8%. For hepatic ablation model, the isotherm underestimated the lesion diameter by 4 %. For short treatment times below 30 s in cardiac ablation, and for long treatment times in hepatic ablation above 20 min, the thermal dose should be used to determine lesion dimensions since the isotherm results in large errors in these cases.