An Adaptive-FocusingAlgorithm for a Microwave Planar Phased- Array Hyperthermia System

• We have experimentally investigated the use of adaptive-focusing techniques in the hyperthermia treatment of cancer. Gradient-search adaptive-focusing software developed at Lincoln Laboratory has been implemented on a commercial microwave hyperthermia planar phased-array antenna system at the University of California at San Francisco (UCSF). The system, manufactured by Labthermics Technologies, Inc., consists of 16 independent amplitude/phasecontrolled waveguide antenna elements operating at 915 MHz. In the experiments, conducted at UCSF, a method of steepest-ascent gradient-search feedback algorithm was used to control the hyperthermia array phase shifters and focus the transmitted radiation beam at a hypothetical tumor site in a muscle-equivalent sugar/saline liquid phantom. A feedback probe, embedded in the phantom, measured the resulting electric field (E-field) generated by the antenna array. The measured data indicate a significant increase in the focal-region field strength with a rapid convergence of the adaptive-focusing algorithm in 10 to 15 iterations. From the measurements, the maximum useful heating depth in thesugarlsaline phantom is estimated for the 915-MHz system at about 3 em.