Instructional design focuses on solving problems in a multitude of contexts. As such, designers are investigators, gathering evidence to optimally design solutions to learning problems within the identified context. The challenge described in this case study was the need to create an educational activity to promote interaction and collaboration among an interdisciplinary participant group comprised of physicians, radiobiologists, and radiation physicists. Based on the premise that interdisciplinary medical research collaboration requires a shared understanding of authentic problems from multiple perspectives, this design research case documents the design and implementation of an online case study incorporating collaborative inquiry in interdisciplinary teams with the intended outcome of building or strengthening interdisciplinary communication skills. Contextual factors - including the design team and design process - influencing the design of the activity are documented. Results indicate that using an interactive online case study as the basis for collaborative inquiry in small, interdisciplinary teams followed by a summative, large group discussion resulted in (1) evidence-based treatment decisions based on the data supplied in the case study and (2) participation of all disciplines in team interactions. Outcomes also indicated the building or strengthening of interdisciplinary communication skills and the understanding of the value and contribution of all three fields to radiation oncology treatment resulted in the participation of the online case study.