IMRT OR VMAT Radiotherapy excluding cervical 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