Ultrasound technology for hyperthermia

Hyperthermia (HT) is used in the clinical management of cancer and benign disease. Numerous biological and clinical investigations have demonstrated that HT in the 41-45 degrees C range can significantly enhance clinical responses to radiation therapy, and has potential for enhancing other therapies, such as chemotherapy, immunotherapy and gene therapy. Furthermore, high-temperature hyperthermia (greater than 50 degrees C) alone is being used for selective tissue destruction as an alternative to conventional invasive surgery. The degree of thermal enhancement of these therapies is strongly dependent on the ability to localize and maintain therapeutic temperature elevations. Due to the often heterogeneous and dynamic properties of tissues, most 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 technology has significant advantages that allow for a higher degree of spatial and dynamic control of the heating compared to other commonly utilized heating modalities. These advantages include a favorable range of energy penetration characteristics in soft tissue and the ability to shape the energy deposition patterns. Thus, heating systems have been developed for interstitial, 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 various shapes and sizes. This article provides a general review of a selection of ultrasound hyperthermia systems that are either in clinical use or currently under development, that utilize these advantages as a means to better localize and control HT for the aforementioned therapies.