Microbiota-guided Radiotherapy for Head and Neck Cancer

Inclusion Criteria: * Age ≥ 18 years. * ECOG Performance Status ≤ 3. * Histological diagnosis of squamous cell carcinoma, undifferentiated carcinoma, epithelial glandular and non-glandular carcinoma (including adenoid cystic carcinoma, adenocarcinoma, mucoepidermoid carcinoma, neuroendocrine carcinoma, etc.) originating from the oral cavity, oropharynx, nasopharynx, hypopharynx, larynx, salivary glands, paranasal sinuses, or from an unknown primary site. * Stage III-IV non-metastatic disease for pharyngeal, laryngeal, or unknown-primary tumors, according to AJCC 7th edition. Patients with stage III-IV tumors of salivary gland or paranasal sinus origin, and patients with stage I-II pharyngeal or laryngeal tumors, will only be included if prophylactic irradiation of cervical lymph node stations is indicated and/or if the oral and oropharyngeal mucosa as well as swallowing-related structures are included within the irradiated volume. * Indication for treatment in either definitive or adjuvant settings, with or without systemic therapy (concurrent systemic therapy, with or without prior neoadjuvant chemotherapy, permitted. Adjuvant systemic therapy is allowed for selected advanced stages of pharyngeal carcinoma, according to institutional guidelines). * Formal acceptance of study participation requirements (written informed consent). Exclusion Criteria: * Prior radiotherapy to the head-neck region. * Presence of connective tissue disorders (e.g., lupus erythematosus or scleroderma) or synchronous head and neck malignancies, except for superficial skin cancers or surgically treated carcinoma in situ not requiring radiotherapy or systemic therapy. * Absence of formal acceptance of study participation requirements (written informed consent). * Indication for treatment exclusively in the postoperative setting.