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.