Head and neck (HN) radiotherapy often requires corrective interventions. This study evaluated three methods for synthetic computed tomography (CT) generation for adaptive HN planning using cone-beam CT (CBCT) images. CBCT images for 15 patients were paired with same-day repeat CT scans and robustly optimized proton plans were recalculated. The anatomy-preserving virtual CT (APvCT) method utilized organs-at-risk as deformation controlling structures. APvCT and conventional virtual CT methods showed lower mean absolute errors in CT number values compared to corrected CBCT; however, all synthetic CT methods were found suitable for proton dose recalculation with gamma passing rates greater than 96.7% (2%, 2 mm).