Abstract: A light delivery catheter having an elongate, flexible inner tube coaxially disposed within a lumen within a flexible outer tube, and axially movable with respect to the outer tube. An optical waveguide disposed within the inner tube conducts light from an external light source to a light diffuser element in optical communication with the distal end of the optical waveguide. A portion of the light conducted to the diffuser element is scattered radially into the surrounding volume. The outer diameter of the inner tube is less than the diameter of the outer tube lumen, the annular space therebetween forming a cylindrical lumen coextensive with the inner tube. One or more fiber optics disposed within the cylindrical lumen are attached to the outer surface of the inner tube and terminate distally in an isotropic tip.