Radiotherapy is the main treatment method for head and neck tumors. However, almost all patients with head and neck tumors will develop acute inflammatory reactions such as Radiotherapy-Induced Oral Mucositis (RIOM) after receiving Radiotherapy, resulting in a decline in the quality of life of patients, hindering the smooth implementation of the treatment plan, reducing the therapeutic effect, and increasing the economic burden of patients. However, the current treatment strategies for RIOM focus on symptomatic treatment and have little impact on the course, severity and related complications of mucositis. Therefore, exploring effective strategies, predicting the incidence and severity of RIOM in patients, and providing prevention and treatment are the clinical bottlenecks and cutting-edge issues that urgently need to be solved in the current clinical practice of radiotherapy for head and neck tumors. Previous studies have shown that the steady-state of metallic elements may be closely related to the occurrence and development of RIOM. Therefore, we plan to conduct a prospective, single-center, observational study to further explore the correlation between metal elements and severe RIOM, analyze its predictive efficacy, and observe the dynamic changes of metal elements in radiotherapy.