Calculation of absorbed power in tissue for various hyperthermia devices

Recently, there has been increased interest in the use of hyperthermia (temperatures, 42 to 45 degrees) as an adjuvant modality to radiation therapy or chemotherapy for the treatment of cancer. This paper discusses the use of the finite element method as a technique for calculating the power deposited per unit volume of tissue for two regional-type hyperthermia devices. The two types of devices investigated are inductive concentric coils and annular phased arrays. The mathematical basis for the finite element method and its advantages when dealing with problems involving irregular boundaries and nonhomogeneous tissue are reviewed. Specific examples are shown for the calculations of the electromagnetic fields and the resulting absorbed power density. Furthermore, it is shown how the basic finite element formulation for the electromagnetic problem can be extended to solving the temperature distribution problem. Temperature distributions for both types of devices are illustrated. Finally, the limitations of the finite element method are reviewed, and possible implications of the specific results for the efficacy of regional devices are raised.