The 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?

In this hybrid type 1 effectiveness-implementation study, the investigators will conduct a stepped-wedge cluster randomized trial with cancer centers (n=4; 484 patients) randomized to sequentially deliver treatment as usual (TAU) then ENDURE to patients with head and neck cancer undergoing surgery and postoperative radiation therapy (PORT). The trial will assess the effect of ENDURE vs TAU on improving initiation of timely PORT (primary objective) and the underlying mechanisms of ENDURE (secondary objective). The investigators will concurrently conduct a mixed-methods study with quantitative measures of implementation outcomes and qualitative data about implementation determinants from semi-structured interviews with key stakeholders and site visits (exploratory objective).

Inclusion Criteria:

1. Age >/= 18 years
2. Squamous cell carcinoma (SCC) (or histologic variant) of the oral cavity, oropharynx, hypopharynx, larynx, unknown primary, paranasal sinuses, or nasal cavity
3. American Joint Committee on Cancer (AJCC) 8th edition clinical T3-4 or >N1 SCC of the oral cavity, oropharynx, hypopharynx, larynx, paranasal sinuses, nasal cavity, or unknown primary.
4. No history of radiation therapy for treatment of HNSCC in the definitive or adjuvant settings that would, at the discretion of the enrolling clinician, affect the patient's need for adjuvant RT.
5. Plan for curative intent surgery at one of the participating centers
6. Plan for PORT (regardless of whether it is at the surgical center) with or without concurrent chemotherapy following curative intent surgery based on the expectation of at least one of the following adverse features on final pathologic evaluation: pT3 or pT4 primary, N1 or greater nodal disease, perineural invasion (PNI), or lymphovascular invasion (LVI).

Exclusion Criteria:

1. Inability to speak or read English or Spanish.
2. Severe mental illness that would prevent trial participation.
3. HPV-positive OPC or unknown primary SCC staged as cT1-2N1 with a single ipsilateral LN < 3 cm
4. Synchronous untreated malignancy expected to impact life expectancy

Below are the key elements of the data sharing plan as outlined in the NIH Policy for Data Management and Sharing:

Research materials will include: (1) self-report measures from patients; (2) clinical data from the electronic medical record; (3) audio recordings and transcriptions of interviews from stakeholders; and (4) field notes from direct observations of the delivery of ENDURE at each site. Data will be raw or minimally processed. The investigators plan to use REDCap for data capture and management of the clinical and self-report measure data and NVivo for management of the qualitative data. REDCap data dictionaries can be distributed for reuse. The final data dictionaries have not been developed. Scientific data and metadata will be generated, preserved, and shared using NIH common data elements. Scientific data and metadata arising from the project will be uploaded to openICPSR, a self-publishing repository for social, behavioral, and health sciences research data.

Data will be shared no later than the time of a publication of findings of the trial's primary endpoint in a peer-reviewed journal.

All data sharing will comply with privacy and confidentiality protections such as the NIH Certificate of Confidentiality and applicable laws, regulations, and policies governing data derived from human participants.