Radiotherapy-Induced Oropharyngeal Mucositis (RIOM) is one of the most distressing side effects for patients with head and neck tumors during radiotherapy, requiring clinical physicians to manage it according to the severity of mucositis to alleviate symptoms and improve quality of life. However, traditional diagnosis of RIOM overly relies on subjective evaluation, lacks early sensitivity, and existing biomarker diagnostic methods suffer from insufficient efficacy, invasiveness, and inconsistent results. This study aims to explore the diagnostic and predictive value of exhaled breathomics in RIOM of head and neck tumors. By collecting exhaled breath samples from head and neck tumor patients undergoing radiotherapy and analyzing volatile organic compounds (VOCs) using breath detection technology, we aim to develop and validate a non-invasive diagnostic and predictive model based on exhaled breathomics. The study will identify specific VOCs as potential biomarkers, providing new tools for early diagnosis, timely prediction, and personalized treatment of RIOM.