Study design and PatientsIn this retrospective study, patients diagnosed with HNSCC received definitive CRT were enrolled in William Beaumont hospital from September 2012 to March 2017. The patients’ data investigated came from a clinical trial “A prospective, non-randomized trial evaluating the utility of adaptive radiotherapy in the management of locally advanced squamous cell carcinoma of head and neck (HNSCC)” (IRB 2012-100). They were eligible for enrollment if biopsy-proved squamous cell carcinoma in head and neck area. Written informed consent was obtained from each patient.