The design and development of intracavitary ultrasound arrays for hyperthermia.

Abstract

This study investigated the design concepts and development of two types of intracavitary ultrasound applicators for use in hyperthermia cancer treatment. Acoustic field calculations, thermal simulations, bench experiments, and in vivo and in vitro studies were utilized to determine and then evaluate the final designs. Each of these devices appears to offer a significant improvement over the existing RF and microwave intracavitary hyperthermia methods. The first type of applicator consisted of a multielement array with the power level to each element independently controlled. This is an important feature in that it allows the power deposition along the length of the array to be modified during a treatment to account for changes in blood perfusion or local heating rates. A temperature regulated water bolus provided acoustic coupling and additional control over the depth of the maximum temperature from the cavity wall. These applicators were tested in vivo and in vitro and were able to induce controlled transrectal heating at depths of 2-3 cm in the canine rectum and prostate gland. The second type of applicator to be developed was an electrically focused array. Computer simulations were used to perform a parametric study of the design of such arrays. These results have indicated that cylindrical arrays of a practical size (7.5 cm long, 1.5 cm O.D.), resonating at 0.5 MHz with individual elements that are up to 1.5 mm wide, can preferentially heat regions 2-5 cm from the array surface. In addition, it was shown that the temperature distribution can be further controlled by scanning the focal position within the target volume, producing heated regions up to 4 cm wide. A practical design was developed and a prototype 0.5 MHz array was constructed and tested in degassed water. These results were in good agreement with the corresponding theoretical simulations.