Design and characterization of an intracavitary ultrasound hyperthermia applicator for recurrent or residual lesions in the vaginal cuff

For evaluating the feasibility of treating recurrent lesions in the vaginal cuff by hyperthermia, a 2-element ultrasound applicator was designed, constructed and characterized. A half-cylindrical transducer (d = 1 cm, length = 1 cm) was used to construct the 2-element ultrasound applicator. Each element of this applicator was operated at 1.5 MHz and characterized by measuring transducer efficiency and acoustic power distribution. Thermocouple probes were used to measure the temperature rise in the phantom. The element sizes used in this study were selected to be comparable to a high dose rate brachytherapy colpostat applicator. Each element was powered separately to achieve a desired temperature pattern in a target. The acoustic output power as a function of applied electric power of elements 1 and 2 were linear over this 1-40 W range and efficiencies were 32.2 ± 3.4% and 46.2 ± 0.8%, respectively. The temperature measurements in the phantom showed that a 6°C temperature rise was achieved 2 cm from the applicator surface. As a conclusion, the ability of the ultrasound colpostat applicator to be used for hyperthermia was demonstrated by measuring acoustic output power, ultrasound field distribution and temperature rise in the phantom. Based on the characteristics of this applicator, it has the potential to be useful for inducing hyperthermia to the vaginal cuff in the clinic.