Many therapists who work with patients who have had a brain injury (BI) include games to ameliorate boredom associated with repetitive rehabilitation exercises. However, designing effective, appropriate, and engaging games for BI therapy is challenging. Following a user-centered approach we created GaPBIT (Game Design Patterns for BI Therapy), a prototype tool that leveraged design patterns to support designer-therapist collaboration when ideating games for BI therapy. We observed the use of GaPBIT in six game ideation workshops that involved game designers and therapists. The tool effectively facilitated collaboration in the interdisciplinary teams. Findings also suggested that information tools like GaPBIT support but do not replace informative collaboration among designers and subject-matter experts (i.e., therapists in our study). We argue that our findings and research methodology generalize to other domains where communication and collaboration among interdisciplinary design teams are imperative for designing "successful" games; i.e. games that meet the varied goals among stakeholders.