Tissue heating during tumor ablation with irreversible electroporation

Exposing biological cells to sufficiently strong external electric fields causes electroporation of cell membranes, i.e. occurrence of transient or permanent permeable pathways between the interior and exterior of the cell. Electroporation can be used to introduce various molecules into cells (reversible electroporation) or to kill cells (irreversible electroporation), which can in turn be used for tissue ablation. The main advantages of irreversible electroporation over other ablation techniques are its non-thermal nature and consequently fast tissue regeneration. For efficient tissue ablation that utilizes its non-thermal nature it is therefore crucial that an adequate electric field distribution is achieved in the target tissue and that the temperature inside the tissue stays below the thermal damage thresholds. This can be achieved by careful positioning of the electrodes with respect to the target tissue and an appropriate choice of the number, duration and amplitude of electric pulses applied during the treatment. We present a treatment planning procedure for planning irreversible electroporation for cancer ablation that uses a sequential model of electroporation and a genetic algorithm-based optimization procedure. We show that it is possible to reduce tissue heating during the optimization procedure by penalizing higher temperatures in the objective function. We also show that optimization of electroporation parameters takes too much time when an accurate calculation of the temperature distribution is performed for each set of parameters. Instead, we propose that heating during electric pulse delivery is only conservatively estimated in the optimization procedure, while an accurate calculation is performed only when the conservative estimate implies the possibility of thermal damage.