Usability evaluations of healthcare technologies are of utmost importance to ensure efficient and safe usage, suitable workload and acceptance. However, number and availability of healthcare professionals that can be involved is limited in many cases. For this reason, Human-Computer Interaction (HCI) professionals are often considered as substitutes of real users by applying usability inspection methods such as heuristic evaluations and cognitive walkthroughs. This study compares the performance of 8 healthcare professionals and 13 HCI professionals in the assessment of the health-related status in follow-up care of patients with head and neck cancers (HNC). For this, a cognitive walkthrough task with an interactive system designed for immediate feedback on therapy progress using patient-reported outcomes was chosen. Results indicate that HCI professionals might misclassify relevance of usability issues due to limited knowledge of the healthcare domain.