Abstract: An apparatus and method for treating an occlusion or constriction, such as a stenosis in a blood vessel or other conduit in the body, as well as an apparatus and method for treating a tumor or cancerous area occurring around a conduit or duct in the body. The apparatus includes a catheter provided with a centering balloon including a catheter centering balloon encircling a portion of the catheter near its distal end. This centering balloon contains a plurality of thin spoke-like members. A second dilatation balloon attached to the surface of the catheter is used to treat the stenosed area. A radioactive source of material is included for treating the stenosis or cancer.