Background: Uterine myomas (fibroids) are the most common pelvic tumors occurring in women, and are the leading cause of hysterectomy. Traditional treatments involve either surgical removal of the uterus, or the fibroids. The goal of this project is to develop and evaluate interstitial ultrasound devices for potential as a minimally-invasive alternative for controlled thermal coagulation of fibroids.

Methods: Multi-element ultrasound applicators were fabricated using tubular transducers, some were sectored to produce 180° directional heating patterns. The devices are inserted in 2.4 mm OD catheters integrated with water cooling. Human uterine fibroids were obtained after routine myomectomies, and instrumented with multi-junction thermocouples spaced at 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 cm from the applicator. Power levels ranging from 8-15 W per element were applied for up to 15 minute heating periods. Temperature data was recorded at 27 points throughout the fibroid, and thermal dose distributions were calculated from the thermal history. The tissue was sectioned after treatment and placed in a 2% TTC tissue viability stain. Measurements of lesion dimensions were obtained from the stained sections. 3D biothermal simulations were performed to investigate applied power levels, treatment durations, perfusion, ability to treat fibroids of various dimensions, and effects of applicator positioning on targeting ability.

Results: Therapeutic temperatures >50° C and cytotoxic thermal doses (t₄₃) greater than 240 min extended beyond 2 cm radially from the applicator. Thermal lesions measuring greater than 1.5-1.7 cm radial depth and up to 5 cm in length were produced in less than 10 min with 15 W of applied power. Simulations indicated that the number of active transducer sections, applied power levels, and directionality can be controlled to preferentially treat large volumes in a short time (e.g., four transducer applicator, 360°, coagulate ~60 cm³, <15 min).

Conclusions: These ultrasound devices offer favorable energy penetration allowing large volumes of tissue to be treated in short periods of time, as well as axial and angular control of heating to conform treatment to a targeted tissue, while protecting surrounding tissues. It is anticipated that this system will make a significant contribution toward minimally-invasive treatment of uterine fibroids.