Electromagnetic optimization of dual mode antennas for radiometry controlled heating of superficial tissue
The large variance of survival in the treatment of large superficial tumors indicates that the efficacy of current therapies can be dramatically improved. Hyperthermia has shown significant enhancement of response when used in combination with chemotherapy and/or radiation. Control of temperature is a critical factor for treatment quality (and thus effectiveness), since the response of tumor and normal cells is significantly different over a range of just a few degrees (41-45°). For diffuse spreading tumors, microwave conformal arrays have been shown to be a sound solution to deposit the power necessary to reach the goal temperature throughout the targeted tissue. Continuous temperature monitoring is required for feedback control of power to compensate for physiologic (e.g. blood perfusion and dielectric properties) changes. Microwave radiometric thermometry has been proposed to complement individual fluoroptic probes to non-invasively map superficial and sub-surface temperatures. The challenge is to integrate the broadband antenna used for radiometric sensing with the high power antenna used for power deposition. A modified version of the dual concentric conductor antenna presented previously is optimized for such use. Several design challenges are presented including preventing unwanted radiating modes and thermal and electromagnetic coupling between the two antennas, and accommodating dielectric changes of the target tissue. Advanced 3D and planar 2D simulation software are used to achieve an initial optimized design, focused on maintaining appropriate radiation efficiency and pattern for both heating and radiometry antennas. A cutting edge automated measurement system has been realized to characterize the antennas in a tissue equivalent material and to confirm the simulation results. Finally, the guidelines for further development and improvement of this initial design are presented together with a preliminary implementation of the feedback program to be used to control the temperature distribution in variable, inhomogeneous tissue.
