This is a prospective, randomized, double-blind, placebo-controlled clinical trial designed to evaluate the efficacy and safety of spirulina supplementation in patients with radiation-induced oral mucositis (RIOM) receiving radiotherapy for head and neck cancer. Participants will be randomly assigned to receive either spirulina tablets or placebo in addition to standard oral care during radiotherapy. The primary objective is to determine whether spirulina reduces the severity of oral mucositis. Secondary outcomes include the incidence and duration of severe oral mucositis, oral pain, nutritional status, quality of life, treatment interruption, and adverse events. The findings of this study may provide evidence for an effective and safe adjunctive intervention to improve the management of radiation-induced oral mucositis and enhance the quality of life of patients undergoing radiotherapy.