A medical device assembly for insertion into a cavity of a patient's body and for delivery of a fluid to and/or retrieval of fluid from the patient's body , comprising: an electromagnetic radiation, EMR, source for providing non-ultraviolet, therapeutic EMR having an intensity comprising a radiant exposure of at least 0.1 J/cm 2 and up to 1.0 kJ/cm 2 and power of at least 0.005 mW and up to 1 Watt, for inactivating one or more infectious agents and enhancing healthy cell growth; a catheter having an elongate catheter body with at least one internal lumen , a coupling end and a distal end , the distal end being insertable into the cavity of the patient's body , wherein the catheter body is configured to direct both the fluid and the therapeutic EMR axially relative to the catheter body , to facilitate at least one of delivery of fluid into the patient's body and retrieval of fluid from the patient's body ; an optical element conducive to the axial propagation of the therapeutic EMR relative to the catheter body , the optical element having a position with respect to the catheter body of being at least one of in, on, or within a wall of the catheter body and within at least one internal lumen of the catheter body , the optical element having an elongate body conducive to the axial propagation of the therapeutic EMR through the elongate body , the elongate body having an exterior surface between a coupling end and a distal end , the exterior surface having at least one radial emission portion , wherein the radial emission portion facilitates the radial emission of therapeutic EMR from the elongate body proximate each radial emission portion ; and at least one coupling to connect the EMR source to the catheter body ; characterized in that the at least one radial emission portion comprises an ablated surface having a gradient ablation pattern. an electromagnetic radiation, EMR, source for providing non-ultraviolet, therapeutic EMR having an intensity comprising a radiant exposure of at least 0.1 J/cm 2 and up to 1.0 kJ/cm 2 and power of at least 0.005 mW and up to 1 Watt, for inactivating one or more infectious agents and enhancing healthy cell growth; a catheter having an elongate catheter body with at least one internal lumen , a coupling end and a distal end , the distal end being insertable into the cavity of the patient's body , wherein the catheter body is configured to direct both the fluid and the therapeutic EMR axially relative to the catheter body , to facilitate at least one of delivery of fluid into the patient's body and retrieval of fluid from the patient's body ; an optical element conducive to the axial propagation of the therapeutic EMR relative to the catheter body , the optical element having a position with respect to the catheter body of being at least one of in, on, or within a wall of the catheter body and within at least one internal lumen of the catheter body , the optical element having an elongate body conducive to the axial propagation of the therapeutic EMR through the elongate body , the elongate body having an exterior surface between a coupling end and a distal end , the exterior surface having at least one radial emission portion , wherein the radial emission portion facilitates the radial emission of therapeutic EMR from the elongate body proximate each radial emission portion ; and at least one coupling to connect the EMR source to the catheter body ; characterized in that the at least one radial emission portion comprises an ablated surface having a gradient ablation pattern. <EOS>