A system and method for treating tissue, such as treating prostate diseases, using an ultrasound therapy system. An ultrasonic applicator (100) has at least one transducer element (102). The steering and focusing of ultrasound beams uses at least one variable focus lens, which may be a fluid focus lens (10), attached to each transducer element so that focus of the variable focus lens is controlled by a voltage signal. A treatment controller (122) receives input from an imaging means (124) and controls the voltage applied to the variable focus lens (10). The treatment controller controls the lens voltage signals, at least partially determined by the input from the imaging means, and directs an ultrasonic treatment beam (26) emitted by the transducer element. Fine adjustment of the therapy beam is achieved to deliver therapy for various prostate sizes and shapes while avoiding damage to critical structures such as the rectal wall and nerve bundles.
