Combination of transurethral and interstitial ultrasound applicators for high-temperature prostate thermal therapy

The purpose of this study was to determine the feasibility of using a trans urethral ultrasound applicator in combination with implantable ultrasound a pplicators for inducing thermal coagulation and necrosis of localized cance r lesions or benign disease within the prostate gland. The potential to tre at target zones in the anterior and lateral portions of the prostate with t he angularly directive transurethral applicator, while simultaneously treat ing regions of extracapsular extension and zones in the posterior prostate with the directive implantable applicators in combination with a rectal coo ling bolus, is evaluated. Biothermal computer simulations, acoustic charact erizations, and in vivo thermal dosimetry experiments with canine prostates were used to evaluate the performance of each applicator type and combinat ions thereof. Simulations have demonstrated that transurethral applicators with 180-270 degrees acoustic active zones can direct therapeutic heating p atterns to the anterior and lateral prostate, implantable needles can isola te heating to the posterior gland while avoiding rectal tissue, and that th e combination of applicators can be used to produce conformal heating to th e whole gland. Single implantable applicators (1.8 mm OD x 10 mm long, simi lar to 180 degrees active sector, similar to 7 MHz, direct-coupled type) pr oduced directional thermal lesions within in vivo prostate, with temperatur es >50 degrees C extending more than 10 mm radially after 10- 15 min. Combi nation of interstitial applicators (1-2) and a transurethral applicator (3- 2.5 mm OD x 6 mm long, similar to 180 degrees active sector, 6.8 MHz, 6 mm OD delivery catheter) produced conforming temperature distributions (48-85 degrees C) and zones of acute thermal damage within 15 min. The preliminary results of this investigation demonstrate that implantable directional ult rasound applicators, in combination with a transurethral ultrasound applica tor, have the potential to provide thermal coagulation and necrosis of smal l or large regions within the prostate gland, while sparing thermally sensi tive rectal tissue.