A Feasibility Study on Adaptive 18F-FDG-guided Radiotherapy for Recurrent and Second Primary Head and Neck Cancer in the Previously Irradiated Territory.

Inclusion Criteria: * Histologically confirmed recurrences and second primary squamous cell carcinoma of the oral cavity, oropharynx, hypopharynx or larynx in the previously irradiated territory. * Primary unresectable tumor and/or patients refused surgery. * No grade 3 or more late toxicity (except xerostomia) after the initial radio(chemo)therapy for primary head and neck cancer. * Minimal interval 12 months after the initial radio(chemo)therapy for primary head and neck cancer. * Decision of a multidisciplinary tumor board on curative radiotherapy (in combination or not with targeted therapy with cetuximab) * Karnofsky performance status ≥70%. * Age ≥ 18 years old. * Informed consent obtained, signed and dated before specific protocol procedures. Exclusion Criteria: * Previous radiotherapy for cT1-2 cN0 M0 glottic cancer. * Brachytherapy as treatment for second primary / recurrence. * Distant metastases. * Other second primary tumors that are not under control. * Pregnant or lactating women. * Elevated blood creatinine level. * Allergy to the CT-contrast agents. * Mental condition rendering the patient unable to understand the nature, scope, and possible consequences of the study. * Patient unlikely to comply with protocol, i.e. uncooperative attitude, inability to return for follow-up visits, and unlikely to complete the study.