Use of vascular and non-vascular models for the assessment of temperature distribution during induced hyperthermia.

We developed a three-dimensional thermal model in which convective heat transfer in a human extremity is explicitly quantified by taking into account the physical details of the vascular system. The spatial pattern in the arterial, venous and tissue temperature is computed during hyperthermia treatment. As such a complex vascular model is not generally applicable, a comparative study of the results of simpler, substitutional, non-vascular concepts applied to hyperthermia was carried out. It turned out that classical bioheat approaches may lead to wrong conclusions. Satisfactory results are to be expected from an approach suggested by Wissler/Baish and Charny/Levin, and by a far simpler efficiency function (EF) concept, developed by us, that can be used as easily as the simple classical Pennes approach while avoiding its deficiencies. The EF model is used to predict whether the temperature of the entire volume of vascularized muscle tissue will be raised to a therapeutic level. With the help of the vascular model, local thermal non-uniformities near individual blood vessels are analysed. Underheating in small volumes of tissue near the vessel walls is detected. This might explain tumour regrowth following local hyperthermia treatment in the tissue adjacent to blood vessels.