Vitamin D Oral Gel for Prevention of Radiation Induced Oral Mucositis

Inclusion Criteria: * Patients who are going to receive radiotherapy as a treatment of head and neck cancer either as postoperative (adjuvant) therapy or definitive therapy. * Patients whose radiotherapy treatment planned dose is 50 Gy or above. * Patients receiving radiotherapy alone or receiving concomitant cisplatin (or carboplatin) with radiotherapy. Exclusion Criteria: * Patients under Anticoagulants such as warfarin, heparin, or aspirin. * Patients whose radiotherapy treatment planned dose is lower than 50 Gy. * Patients suffering from any uncontrolled systemic diseases (such as diabetes, cardiovascular, liver disorder, renal dysfunction) * Patients with findings of any physical or mental abnormality which would interfere with or be affected by the study procedure. * Hyper-calcemic patients. * Smokers.