This invention pertains a system and methods for ablation treatment of tissues. The invention aims to improve current models that allow predicting the volume and geometry of thermal ablations. Particularly the invention consists in a method that allows accounting for effects that occur when vapor that forms at the ablation site is able to seep in cavities that might encroach the ablation site and to deliver heat to the tissues of those cavities, creating an ablation geometry that is not described by current ablation models.