Temperature Focusing in Microwave Cancer Hyperthermia via Pre-Corrected SAR-Based Focusing
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Microwave hyperthermia aims at selectively heating cancer cells to a supra-physiological temperature. For internal tumors, this is currently achieved by means of an antenna array equipped with a proper cooling system (the water bolus) to avoid overheating of the skin. The planning of the administered heating is usually tackled by finding the antenna feedings that maximize the specific absorption rate (SAR) inside the tumor. However, it might happen that an optimal power deposition on the target does not lead to an equally satisfying temperature focusing. In this paper, we discuss that this is due to the thermal boundary conditions dictated by the external cooling system, and we propose a strategy to overcome this effect. The procedure is still phrased in terms of an optimization of the SAR, but with an additional algorithm to determine a corrected SAR focusing location that maximizes the actual temperature coverage of the tumor. The procedure is thus applicable to existing SAR-based planning approaches; it involves multiple, parametric solutions of the bioheat equation, and appears to require a very limited computational load. Application of this strategy to a tumor in the 3D head and neck region is presented to show the effectiveness of the approach.
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