Performance of a multi-sector ultrasound hyperthermia applicator and control system: in vivo studies

A multi-element ultrasound hyperthermia system (Labthermics Technologies, Inc., Sonotherm 1000) was utilized to deliver energy to two relatively well-defined regions (3 × 8 × 3 × 8 cm) on the lateral aspect of the right rear leg of 22 dogs in 1, 2 and 3 weekly treatments to a target temperature of 42-43°C, at a depth of 1 cm. The total treatment time was 30 min. One area heated on each dog was adjacent to the proximal femur and the other was 2-3 cm away from the distal aspect of the same bone. The system performed in an acceptably controlled manner and was able to deliver energy to a well-defined site. The mean temperature achieved, and rate of temperature rise in the heated regions, was independent of the region being treated. Little difference (0·12°C) was noted between the mean temperatures of the heated regions, and the temperature bounds (42-43°C) were exceeded by a small amount and for a relatively short period of time (out of range RMSE=0·6°C). Unheated regions showed much lower mean temperatures than did heated regions located 3 · 8 cm away, indicating that the energy was delivered in a well-defined manner. Superficial thermal injuries occurred in three of 22 dogs in the area heated 2-3 cm away from bone, and 11 of 22 dogs exhibited injuries in the tissue heated immediately adjacent to the femur.