An ultrasound applicator for thermal therapy, having a multi-element array of plastic or rubber coated piezoceramic tubular transducers, each with separate power control and supported by a coaxially disposed semi-flexible central tube, which can be placed directly within the tumor or target region, or within a body lumen such as a blood vessel or body cavity such as the urethra, or within a separate delivery catheter or system. Thermocouple sensors embedded in the coating over each transducer can be used for continuous monitoring of the tissue/applicator interface temperatures for feedback control of the power applied to each transducer. The transducers are resonant across the wall thickness and radiate energy in the radial direction. The applicator provides an air-cooling system which can control the temperature of the transducers and thereby improve heating characteristics. In the primary configuration, the central tube is a catheter which is compatible with remote afterloaders and standard brachytherapy technology, and facilitates the delivery of interstitial thermal therapy in conjunction with simultaneous brachytherapy or radiotherapy from within the applicator. For alternate forms of therapy or when the radiation source is not in the catheter, the central catheter can be used to circulate temperature regulated air or water to control the surface temperature of the applicator, or to infuse drugs. Further, the applicator can be placed within a thin-walled implant catheter and flushed with temperature controlled circulating coupling fluid to control the temperature of the catheter/tissue interface, or used in conjunction with other conventional delivery systems, instead of being used interstitially.