NEW ULTRASOUND PHASED ARRAY APPLICATORS FOR HYPERTHERMIA

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Hyperthermia, particularly when used in conjunction with ionizing radiation, is becoming a viable modality for cancer treatment. A high percentage of the clinical data currently available were obtained with applicators allowing little control of heating patterns within the treatment volume. However, such control is essential for obtaining therapeutically optimum temperature distributions, particularly when blood flow changes during treatment. We propose to continue development of new phased array concepts for ultrasound hyperthermia applicators which should provide the needed heating flexibility. This project has two primary goals: 1. To take the ultrasound phased array technology and prototype systems developed in the first grant period into the clinic, and 2. To continue development of phased array technology with close cooperation with our clinical colleagues. Clinical trials of site-specific phased array systems will be carried out on human patients under a consortium arrangement at Duke University. Development of new technology will be closely tied to actual clinical requirements. With the primary goal of enhancing clinical tumor heating capabilities, we will continue the development of: 1. Conformable or flexible arrays allowing placement and synthesis of optimal apertures for site-specific therapy; 2. Algorithms for allowing simultaneous use of multiple windows into a treatment volume; 3. Algorithms to allow automatic real time correction for patient breathing and movement; and 4. Algorithms to allow real-time phase aberration corrections due to tissue inhomogeneities. Achievement of these first four goals will be aided by development of small invasive hydrophone probes to obtain acoustic feedback from a treatment volume. This approach for phase error correction has been developed in our laboratory and its application has resulted in measured array field patterns which agree remarkably well with theoretical predictions. As additional enhancements to the clinical application of these arrays, we will also develop; 5. Patient treatment planning software which allows mapping of all available windows into a treatment volume onto a computed image of the body surface or array aperture; 6. Modifications of acoustic and thermal modelling algorithms we have previously developed to allow, from specification of desired temperatures at discrete control points, computation of the magnitude and phases for all the array element driving signals, and 7. VLSI chips to reduce the multichannel digital phase synthesis networks to a single computer controlled chip serving 64 channels.