TRIPAS: a triapplicator system with relocatable 'hot spot' at tissue depth.

Solving the problem of heat focusing and standardization of the clinical application of hyperthermia requires a mathematical prediction model. The model should include the medium constitutive parameter, and be able to predict positioning of the microwave applicators to optimize treatment planning and provide for reproducible treatment set-up. We present a configuration of 3 applicators subtended by an equilateral triangle in order to target and relocate a 'hot spot' for improved treatment of deep tumors. A simple geometric analysis is illustrated. The microwave beam absorption profile, from the three power sources, was obtained from phantom studies depicting the radiative heat pattern for the triapplicator system (TRIPAS). A complex mathematical model was developed to demonstrate interaction of the beams in the medium. It was observed empirically that under coherent propagation in the near field electromagnetic (EM) waves tend to add at the center, while varying the propagation axial focal length caused a relocation of the summing focal points. Mathematical prediction correlated very well with the phantom studies. SAR values above 100 W/kg were achieved at 12.5 cm phantom depth, creating a relocatable 'hot spot' at the concentric foci of the 3 air cooled horn microwave applicators operating at 300 MHz.

A computer simulation of simultaneous heat and oxygen transport during heterogeneous three dimensional tumor hyperthermia.

Hyperthermia is a developing modelity for the treatment of cancer. This therapy is occasionally used by itself, however, usually it is used as an adjuvate with chemo or radiation therapy. The mechanism for this treatment is based on the fact that cancer cells are heated preferentially by heat application due to lower vascularity in the tumor tissue as compared with the surrounding normal tissue and that, when used with radiation therapy or chemo therapy, higher oxygen partial pressure in the tumor results in increased tumor cell damage. Appropriate mathematical models and their real time prediction of oxygen and temperature profiles could be very helpful in achieving optimal results via hyperthermia and to avoid possible danger which might occur during the treatment. Because of the complexity and the heterogeneous nature of physiological system, it is necessary to include heterogeneous properties in the mathematical models for them to be useful for biomedical calculations. Of course, it is much more difficult to solve mathematically the heterogeneous system than the homogeneous one. In this paper, the importance of the implementation of heterogeneities in the heat and mass transport for biological system mathematical modelling is discussed. Results of a three dimensional computer simulation of mass and heat transfer in tumor tissue with different capillary geometries during hyperthermia are demonstrated. The method used for the computer simulation is a deterministic/probabilistic technique, Williford-Bruley calculational strategy.

Changes in tissue oxygenation and acidity induced by localized microwave hyperthermia and hematoporphyrin phototherapy, an update.

Changes in tumor tissue oxygenation and acidity were determined using ultramicroelectrodes, and presented in histogram fashion. The effect of Hyperthermia and Hpd photo-therapy were tested. It was found that both modalities affect tumor microcirculation, causing a marked drop in oxygen availability. Tissue pH is decreased by Hyperthermia, but not by phototherapy. These effects are long lasting, at least for 24 hours after treatment.