Oral mucositis (OM) is recognized as one of the most frequent debilitating sequela encountered by head and neck cancer (HNC) patients treated by radiotherapy. The objective of the study is to assess primarily the effect of topical oral Omega-3 hydrogel in prevention of radiation-induced oral mucositis and secondarily, to test the effect of topical oral Omega-3 hydrogel on oral microbiome.

Inclusion Criteria:

1. Patients who are going to receive radiotherapy as a treatment of head and neck cancer either as postoperative (adjuvant) therapy or definitive therapy.
2. Patients whose radiotherapy treatment planned dose is 50 Gy or above
3. Males and females with an age not less than 18 years
4. Patients receiving radiotherapy alone or receiving concomitant cisplatin (or carboplatin) with radiotherapy.

Exclusion Criteria:

1. Patients under Anticoagulants such as warfarin, heparin, or aspirin.
2. Patients suffering from any uncontrolled systemic diseases (such as diabetes, cardiovascular, liver disorder, renal dysfunction)
3. Patients with findings of any physical or mental abnormality which would interfere with or be affected by the study procedure.