A method of using ultrasound waves that are focused at a specific location in a medium is provided to cause localized production of bubbles at that location and to control the production, and the cavitational and heating effects that take place there. Production and control are accomplished by interference-specific waveforms at the focal point, which are not produced at other locations. Preferably, the region within the focal zone of all the transducers in which the specific waveform develops at significant intensities are very small. The method, and a system that performs the method, can be used to perform a variety of therapeutic procedures. Typical of such procedures is occlusion of varicose veins.