Personalized Volume-deescalated Elective Nodal Irradiation in Oropharyngeal Head and Neck Squamous Cell Carcinoma

Inclusion Criteria: * Patients with a newly diagnosed (no pre-treatment) squamous cell carcinoma of the oropharynx (i.e. tonsils, base of tongue, oropharyngeal walls, oropharyngeal surface of epiglottis; ICD-10 codes C01, C09, C10), T1-4, N0-3. * Treatment with definitive (chemo) radiotherapy planned, with elective irradiation of the lymph nodes. * Age ≥ 18 years, no upper age limit. * ECOG performance score \< 3. * History/physical examination within 30 days prior to study inclusion by head and neck surgeon and/or radiation oncologist. * FDG-PET scan prior to study inclusion. In case of inability to perform or contra-indication, at least contrast enhanced MRI scan obligatory. * Participants need to provide informed consent. Exclusion Criteria: Inclusion Criteria: * Patients with a newly diagnosed (no pre-treatment) squamous cell carcinoma of the oropharynx (i.e. tonsils, base of tongue, oropharyngeal walls, oropharyngeal surface of epiglottis; ICD-10 codes C01, C09, C10), T1-4, N0-3. * Treatment with definitive (chemo) radiotherapy planned, with elective irradiation of the lymph nodes. * Age ≥ 18 years, no upper age limit. * ECOG performance score \< 3. * History/physical examination within 30 days prior to study inclusion by head and neck surgeon and/or radiation oncologist. * FDG-PET scan prior to study inclusion. In case of inability to perform or contra-indication, at least contrast enhanced MRI scan obligatory. * Participants need to provide informed consent. Exclusion Criteria: * Multilevel primary tumors extending unambiguously beyond the oropharynx into the oral cavity, naso- or hypopharynx * Distant metastases detected. * Previous surgery, chemotherapy or radiotherapy treatment for other head and neck cancers. * Previous surgery in head and neck region affecting the cervical lymphatic system. Dissection of singular lymph nodes for diagnostic purposes before treatment start is allowed. * Synchronous or previous malignancies. Exceptions are curatively treated basal cell carcinoma or SCC of the skin, or in situ carcinoma of the cervix uteri, low- or intermediate- risk prostate cancer or breast with a progression-free follow-up time of at least 3 years without any remaining disease burden, or other previous malignancy with a progression-free interval of at least 5 years without any remaining active/progressive disease burden regardless whether the treatment is completed or ongoing as a maintenance treatment (e.g. androgen deprivation therapy for prostate cancer). * Pregnancy or breast feeding * Any severe mental or psychic disorder affecting decision making and ability to provide informed consent.