It has been shown that hypoxic tumor cells are resistant to radiation and that increasing tumor oxygen levels via laser-mediated hyperthermia treatment increases tumor cell radiosensitivity. Hence, studies of the effects of laser irradiation on tumor oxygen levels are of great interest, as they allow for the optimization of hyperthermia treatment. Accordingly, the main purpose of this experiment was to develop a finite element model to simulate the heat transfer due to laser irradiation of tumor tissue, the blood flow through a tumor capillary, and the effect of changing temperature on blood flow rates and oxygen delivery to tumor tissue. This was achieved by using finite element models in COMSOL Multiphysics. We employed two geometries based on those used in a simliar study by He et al. [1]: a tumor-containing breast model to simulate laser heating of the tissue and a capillary and tumor tissue model to simulate the effect of heating on blood flow and tissue oxygen concentration. By plotting partial pressure of oxygen as a function of radius at three different points in the tissue, we observed that the oxygen concentration was greatest near the inlet and lowest near the outlet (as expected), and that at all points in the tissue, heating increased the tissue oxygen partial pressure to about the same extent (0.75 ? 1 mm Hg). Furthermore, sensitivity analyses suggested ambient air cooling at the breast surface to be ideal and a laser intensity of 18000 W/m2 to be optimal for hyperthermia treatment. The model we developed was validated by comparison to a similar model and has potential for use in future studies on optimization of hyperthermia treatment.