Ultrasound technology for hyperthermia

Hyperthermia (HT) is used in the clinical management of cancer and benign d isease. Numerous biological and clinical investigations have demonstrated t hat HT in the 41-45 degrees C range can significantly enhance clinical resp onses to radiation therapy, and has potential for enhancing other therapies , such as chemotherapy, immunotherapy and gene therapy. Furthermore, high-t emperature hyperthermia (greater than 50 degrees C) alone is being used for selective tissue destruction as an alternative to conventional invasive su rgery. The degree of thermal enhancement of these therapies is strongly dep endent on the ability to localize and maintain therapeutic temperature elev ations. Due to the often heterogeneous and dynamic properties of tissues, m ost notably blood perfusion and the presence of thermally significant blood vessels, therapeutic temperature elevations are difficult to spatially and temporally control during these forms of HT therapy. However, ultrasound t echnology has significant advantages that allow for a higher degree of spat ial and dynamic control of the heating compared to other commonly utilized heating modalities. These advantages include a favorable range of energy pe netration characteristics in soft tissue and the ability to shape the energ y deposition patterns. Thus, heating systems have been developed for inters titial, intracavitary, or external approaches that utilize properties such as multiple transducer arrays, phased arrays, focused beams, mechanical and /or electrical scanning, dynamic frequency control and transducers of vario us shapes and sizes. This article provides a general review of a selection of ultrasound hyperthermia systems that are either in clinical use or curre ntly under development, that utilize these advantages as a means to better localize and control HT for the aforementioned therapies. (C) 1999 World Fe deration for Ultrasound in Medicine & Biology.