Physics and Physiology of Thermal Ablations

Abstract

The role of ablation in tumor management is increasing. Ablation modalities (Fig. 1.1) differ with respect to mechanism of action, but all share the goal of permanent cell death within the target tissue. Radiofrequency ablation is based upon the application of alternating electric current which is delivered to the target tissue through ablation electrode(s) resulting in frictional tissue heating and ultimately coagulative necrosis. Microwave ablation is based upon the generation of an oscillating electromagnetic field resulting in continuous realignment of polar water molecules in the ablation zone which causes frictional tissue heating and ultimately coagulative necrosis. Cryoablation is based upon the infusion of a cryogen, a gas that cools as it expands, into a cryoprobe resulting in creation of ice via the Joule-Thomson effect, with resultant coagulative necrosis of the target tissue. Irreversible electroporation (IRE) is a non-thermal ablation technique that permanently creates nanoscale defects in the cell membrane by exposing cells to short and intense electric fields, leading to cell death. The published experience with each ablation modality differs, as do cost, ease of use, and treatment outcomes (Table 1.1).