Applicators for generating ultrasound-induced hyperthermia in neoplastic tumours and for use in ultrasound physiotherapy.

Ultrasound in the low megahertz frequency range is used by physiotherapists to treat a variety of conditions. The treatments reduce swelling, reduce pain and increase movement at joints. Ultrasound is now also beginning to be used to treat malignant tumours. The tumours are heated to temperatures between 42 degrees and 45 degrees C, producing cellular damage, the extent of which is determined by the duration and number of treatments and 'concurrent' treatments by chemo and x-ray therapy. In the light of the results of computer simulation, we discuss in this paper: (a) The properties of a five-element divergent transducer array to treat large superficial neoplastic tumours. The field distribution measured by the Sarvazyan method will be described and also compared with that of computer simulation. The benefits of frequency wobbling will also be discussed. (b) The possibility of employing a multiple field applicator for use by physiotherapists to obviate the need for continuous movement of a small transducer of area approximately 5 cm2 over the affected area.