The Effect of Vascularization and Tissue Type on Cryosurgical Procedures
Magleby, Reed; Schallop, Amanda; Shulman, Eric; Sterling, Joshua
Cryosurgery is a minimally-invasive surgical procedure that is used in the treatment of multiple types of cancer. Although cryosurgical treatments, which involve the application of extreme cold to diseased or cancerous tissue, are often used in the treatment of near-surface skin cancer, they have also been used to treat several other types of internal cancers, including those in the prostate, liver, and kidney. Although fundamentally similar, many of these tissues differ significantly in properties such as density, vascularization, and thermal conductivity. A major issue in cryosurgery is adapting the procedure to different tissue types. In this study, the effect of tissue perfusivity on the outcomes of cryosurgery was modeled using the COMSOL software. For the purposes of comparison, the properties of lung tissue, which is highly perfused and not as conductive, and liver tissue, which is mildly perfused and more conductive, were used. The procedure was modeled as a 10 mm diameter cryoprobe set at a temperature of -196?C in a cylindrical region of tissue 8 cm in height and 8 cm in diameter. The time required for a 26mm diameter spherical tumor to reach -45?C was determined in four scenarios, lung tissue and liver tissue both with and without blood perfusion. Although metabolic heat generation was also included, sensitivity analysis showed it to be a minor factor in the cooling process. Results showed blood perfusivity to have a significant effect on freezing time in lung tissue and a relatively minor one in liver tissue: although the addition of perfusion caused freezing time in the liver to increase from 200 to 250 seconds, the addition of perfusion in the lung tissue caused the freezing front to never reach the tumor edge. Sensitivity analyses also revealed the freezing process to be highly sensitive to conductivity as well. It was therefore concluded that although blood perfusion is one of the most important heat transfer processes in cryosurgery, tissue conductivity is just as, if not more important. We recommend that cryosurgery continue to be used as a treatment for liver tumors, but further studies are needed to determine its efficacy in highly perfused, porous tissue such as the lung.
Cryosurgery; Lung Cancer; Vascularization