Abstract: A system for irradiation of a vascular space and its contents is presented. An adapter device having a vascular access end and an optical interface end can include a waveguide affixed within a waveguide lumen and extending outwardly through the vascular access end. The optical interface end includes a tapered terminus configured to engage with a cavity of an optical connector adapter, creating an optical interface between the waveguide of the adapter device and a waveguide of a light or radiation source. The adapter device enables the simultaneous administration of radiation and exogenous fluids to a patient while maintaining the optical interface isolated from any fluids.