Advances in Microwave Hyperthermia Treatment using Time Reversal

University dissertation from Chalmers University of Technology

Abstract: The last twenty years have seen many clinical studies showing the ability of hyperthermia to remarkably enhance response to radiation therapy and chemotherapy. The objective of hyperthermia treatment is to raise the temperature in tumors to therapeutic levels, for a sufficient period of time, in order to achieve cell death or render the cells more sensitive to ionizing radiation and/or chemotherapy. One of the challenges in hyperthermia is to adequately heat deep-seated tumors while preventing surrounding healthy tissue from undesired heating and damage. In this thesis, a new focusing technique, based on a time-reversal (TR) approach, for microwave hyperthermia is described and evaluated. First, the method was tested numerically using 2-D computer models of breast and neck. The obtained results were encouraging and suggest a multifrequency approach, in which the choice of frequency depends on the treated area size as well as on the tumor volume. Building on these results, a specific broadband antenna array was designed. In this design the applicator is immersed in a matching liquid and consists of between 12 and 16 identical triangular patch elements placed in a ring antenna arrangement. Next, we built a TR-hyperthermia amplifier system that operates in both continuous and pulsed wave regimes. The accuracy of the signal delivery as prescribed by the treatment planning tool is similar to clinical standards. However, at present, the output power allows only for experiments with phantoms or animals. The results show great promise and will be further investigated in clinical studies. Finally, the feasibility of microwave thermal imaging as a non-invasive approach for temperature monitoring during the treatment was investigated. The initial results of this approach, which is based on the variation of the dielectric properties with temperature, are encouraging. Work is in progress to evaluate the prospects of integrating microwave thermometry into our TR-hyperthermia system.

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