A medical device assembly, the medical device assembly comprising: 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 directs both the fluid and the sterilizing or therapeutic EMR axially relative to the catheter body, axial flow of the fluid within the catheter body facilitates at least one of delivery of fluid into the patient's body and retrieval of fluid from the patient's body inserted 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, the elongate catheter body further having, in use, an external to the patient's body segment portion and an indwelling portion [180, 182]; an electromagnetic radiation source for providing non-ultraviolet, sterilizing or 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, such intensity being sufficient to produce a therapeutic effect of inactivating one or more infectious agents; an EMR conduction system insertable into the catheter and comprising 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 within at least one internal lumen of the catheter body, at least a portion of the optical element comprises a fiber optic for disposition within the at least one internal lumen of the catheter, the fiber optic comprises a fiber body having an exterior surface, a coupling end, a distal end, and a core, the fiber optic being conducive to the axial propagation of sterilizing or therapeutic EMR within the core relative to the external segment portion and the indwelling portion [180, 182] of the elongate catheter body, the fiber optic further comprises at least one radial emission portion disposed between the coupling end of the fiber body and the distal end of the fiber body, the radial emission portion allowing the emission of sterilizing or therapeutic EMR radially from the fiber body into the internal lumen of the catheter; at least one coupling to connect the EMR source to the EMR conduction system; and characterized in that the medical device assembly is adapted to deliver through the at least one radial emission portion controlled relative intensity of sterilizing or the therapeutic EMR to produce a desired therapeutic effect in, on, or around the external to the patient's body segment portion or the external to the patient's body segment portion and the indwelling portion [180, 182] of the elongate catheter body. 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 directs both the fluid and the sterilizing or therapeutic EMR axially relative to the catheter body, axial flow of the fluid within the catheter body facilitates at least one of delivery of fluid into the patient's body and retrieval of fluid from the patient's body inserted 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, the elongate catheter body further having, in use, an external to the patient's body segment portion and an indwelling portion [180, 182]; an electromagnetic radiation source for providing non-ultraviolet, sterilizing or 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, such intensity being sufficient to produce a therapeutic effect of inactivating one or more infectious agents; an EMR conduction system insertable into the catheter and comprising 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 within at least one internal lumen of the catheter body, at least a portion of the optical element comprises a fiber optic for disposition within the at least one internal lumen of the catheter, the fiber optic comprises a fiber body having an exterior surface, a coupling end, a distal end, and a core, the fiber optic being conducive to the axial propagation of sterilizing or therapeutic EMR within the core relative to the external segment portion and the indwelling portion [180, 182] of the elongate catheter body, the fiber optic further comprises at least one radial emission portion disposed between the coupling end of the fiber body and the distal end of the fiber body, the radial emission portion allowing the emission of sterilizing or therapeutic EMR radially from the fiber body into the internal lumen of the catheter; at least one coupling to connect the EMR source to the EMR conduction system; and