Heating characteristics of a helical microwave applicator for transurethral hyperthermia of benign prostatic hyperplasia.

A new applicator for intraurethral hyperthermic treatment of benign prostatic hyperplasia is described. The applicator uses an insulated helical antenna wound on the outer surface of a silicone urological (Foley) balloon catheter. The balloon catheter assures rapid and reproducible localization of the antenna in the prostatic urethra. Two small cannulae are fixed to the exterior surface of the applicator. One holds a temperature control sensor at a fixed location, the other is used to map temperature along the applicator. Two-dimensional SAR and steady-state temperature distributions measured in a plane tangent to the applicator in a tissue-equivalent phantom are presented, as well as longitudinal temperature distributions measured in situ at the applicator-urethral interface. Prostatic temperatures were also measured intraoperatively. The applicator appears to be capable of elevating temperature to greater than 42 degrees C in a cylindrically symmetric volume of about 4 cm length and about 0.5 cm radial penetration surrounding the antenna. The heating characteristics of this applicator are similar to an earlier design that employed an array of three dipoles. The helical applicator is narrower, more flexible and simpler to use than the earlier design.