This single-center randomized controlled trial evaluates the effects of cold (15-20°C) versus room-temperature (30-35°C) water gargling on oral mucositis severity, pain, and comfort in patients with head and neck cancer undergoing radiotherapy. Participants will rinse their mouth four times daily for 30-60 seconds over a 6-week radiotherapy course, with follow-up for two additional weeks. The study hypothesizes that cold-water rinsing can reduce the severity of radiation-induced oral mucositis (RTOM) and pain, improve oral comfort, and minimize treatment interruptions.

Radiation-induced oral mucositis (RTOM) is a frequent and debilitating side effect of radiotherapy for head and neck cancer, leading to pain, nutritional compromise, and potential treatment discontinuation. Cryotherapy and local temperature modulation have been proposed as low-cost, accessible nursing interventions that reduce inflammation through vasoconstriction and analgesia. This randomized trial will assess the clinical efficacy and patient acceptability of temperature-modulated water rinsing as a non-pharmacologic, supportive-care intervention. Subgroup analyses will examine differential responses among patients with dental sensitivity or betel-nut chewing habits.

Inclusion Criteria:

• Histologically confirmed head and neck cancer (HNC) receiving radiotherapy for the first time, with or without concurrent chemotherapy.
• Conscious, communicative, and able to perform the rinsing procedure and complete questionnaires.
• Provided written informed consent prior to enrollment.

Exclusion Criteria:

• Non-HNC diagnoses or radiotherapy to sites outside the oral/oropharyngeal region.
• Cognitive impairment or inability to complete the rinsing protocol.