RecruitingBehavioural interventionMulti-Site Trial of Navigation vs Treatment as Usual to Improve Initiation of Timely Adjuvant TherapyThe goal of this clinical trial is to compare the effectiveness of a navigation-based multilevel intervention (ENDURE) with treatment as usual (TAU) to improve the initiation of guideline-adherent postoperative radiation therapy among patients with head and neck cancer. The main questions the trial aims to answer are: 1. Does ENDURE improve initiation of timely PORT relative to treatment as usual? 2. What are the mechanisms through which ENDURE improves timeliness to treatment? 3. What are the barriers and facilitators to the implementation of ENDURE into routine clinical care?