Numerical investigation of the effect of vessel size and distance on the cryosurgery of an adjacent tumor.

Cryosurgery is an efficient cancer treatment which can be used for non-invasive ablation of some internal tumors such as liver and prostate. Tumors are usually located near the large blood vessels and the heat convection may affect the progression of the ice ball. Hence it is necessary to predict the surgery procedure and its consequences earlier. In spite of the recent studies it is still unclear that which arteries will significantly affect the freezing treatment of tumors and which can be ignored. Therefore a numerical model of a spherical 3 cm diameter liver tumor, subjected to cryosurgery was developed. The specific thermophysical properties were applied to the tumor and healthy tissues in frozen and unfrozen states. A simplified Hepatic artery with different anatomical diameters was placed in different positions relative to the tumor and energy and momentum equations were solved. The temperature distribution and the shape of the resultant ice ball were discussed. The results showed that a 4 mm diameter artery in the vicinity of a tumor will increase the minimum temperature achieved at the tumor boundary by 12.5 °C and therefore significantly affects the cryosurgery outcome. This may cause insufficient freezing which leads to incomplete death of tumor cells, failure of the surgery and tumor regenesis. Eventually it was shown that injection of gold and FeO nanoparticles to the surrounding tissue of the artery can enhance the heat transfer and progression of the ice ball, making temperature distribution similar to the no vessel state. Development of computational models can provide the physicians an applicable tool which helps them recognize how efficient a treatment method will be for a specific case and design a suitable cryosurgery plan.