The feasibility of interstitial ultrasound hyperthermia

One of the most promising ways to increase the efficacy of brachytherapy is to combine it with hyperthermia. In this paper, the feasibility of using ultrasound transducers as interstitial hyperthermia sources was investigated. The ultrasound output of eight cylindrical transducers (diameter 1 mm and length 25 mm) was studied. It was found that many of these transducers were able to generate between 2 and 3 W of acoustic energy at the frequency of 9.5 MHz. The ultrasound field emitted radially was well collimated and extended the full length of the transducer. In vitro perfused liver and kidney experiments showed that an array of four transducers placed in brachytherapy catheters up to a maximum spacing of 20 mm in a square pattern could induce therapeutic temperatures. Also, the effect of flow rate into the organs and catheter cooling were investigated. These results showed that interstitial ultrasound sources are potentially the most promising way of generating therapeutic temperatures through standard interstitial radiation therapy catheters.