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 X 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 degrees 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 degrees C) was noted between the mean temperatures of the heated regions, and the temperature bounds (42-43 degrees C) were exceeded by a small amount and for a relatively short period of time (out of range RMSE = 0.6 degrees 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.