CLEAR (Cervical Lymphatic Exclusion in Adjuvant Radiation)

The goal of this clinical trial is to learn if selectively omitting postoperative cervical irradiation is a safe and feasible treatment strategy for patients with resected, locally advanced squamous cell carcinoma of the head and neck (HNSCC) who underwent systematic neck dissection and have no high-risk nodal factors. The main questions it aims to answer are: * Is the regional recurrence rate with selective omission of postoperative cervical irradiation non-inferior to the recurrence rate reported with standard complete nodal irradiation (6-8%)? * Does selective omission of postoperative cervical irradiation reduce toxicity? * Does selective omission of postoperative cervical irradiation improve immunological preservation and quality of life? Researchers will compare outcomes in participants treated with this selective irradiation strategy to previously published data and to a retrospective institutional cohort treated with standard complete nodal irradiation, to see if it maintains regional control while reducing toxicity and preserving immune function and quality of life. Participants will: * Receive postoperative radiotherapy according to the new protocol, omitting irradiation of low-risk nodal levels * Receive concomitant chemotherapy if clinically indicated, per standard practice * Visit for checkups, blood sample collection, to complete quality-of-life questionnaires and attend follow-up visits over 48 months

Inclusion Criteria: * Patients ≥ 18 years of age * ECOG Performance Status (PS) ≤ 2 * Histologically confirmed diagnosis of locally advanced squamous cell carcinoma of the oral cavity, oropharynx, hypopharynx, or larynx * Resection of the primary tumor and unilateral and/or bilateral neck dissection performed according to standard guidelines, with detailed histological reporting by nodal level * Number of lymph nodes per dissected neck ≥ 18 * No pathological lymph nodes following neck dissection (pN0) * Presence of a single pathological cervical lymph node following neck dissection (pN1), provided that: * No extracapsular extension * Diameter \< 1 cm * No skip metastasis * Presence of risk factors indicating postoperative radiotherapy. Stages pT1-pT2N1 and pT3-pT4N0/N1. If N1, all of the following criteria must be met: presence of a single cervical lymph node without extracapsular extension, diameter \< 1 cm, and no skip metastasis * Patients may receive adjuvant systemic treatment if surgical margins are positive or close (\< 5 mm) Exclusion Criteria: * Absence of informed consent * Prior irradiation to the head and neck region * Prior surgery in the head and neck region * Contralateral neck dissection not performed when clinically indicated * History of malignancy within the previous 5 years, with the exception of non-melanoma skin cancer * Interval between surgery and radiotherapy \> 8 weeks