Radiation therapy remains the principal treatment for nasopharyngeal carcinoma (NPC). The most frequently occurred radiation-related side effect is probably the radiation-induced oral mucositis (OM), which affects up to 100% of NPC patients receiving radiation therapy. When severe, oral mucositis increases the risk of infection and may compromise clinical outcomes by necessitating treatment breaks, dosage reductions, and reduced therapy compliance. In China, a quadruple mixture, composed of dexamethasone, gentamicin, vitamin B12, and procaine, is commonly prescribed when NPC patients begin to suffer from radiation-induced OM. However, the incidence of radiation-induced OM is still quite high. Oral Ulcer Gargle (FORRAD®) is a proprietary viscous liquid mucoadhesive hydrogel formulation. It creates a palliative barrier over injured mucosa, to prevent and to cure radiation-induced OM. The objective of this randomized phase II study is to assess the efficacy and safety of Oral Ulcer Gargle (FORRAD®) as an intervention for radiation-induced OM in the treatment of NPC, compared with the commonly used quadruple mixture, which is composed of dexamethasone, gentamicin, vitamin B12, and procaine.