The purpose of this study is to assess the clinical utility and safety of Fentanyl for pain treatment caused by radiotherapy. Fentanyl is a synthetic pure opioid agonist with a selective activity on µ receptors.

The study is a phase IV, open label, single arm study. The purpose of this study is to assess the clinical utility and safety of fentanyl transdermal therapeutic system (patch) for treatment of pain caused by radiotherapy. The patients increase or even decrease the amount of study medication in order to achieve pain relief, 48 to 72 hours or 3 days are required after the first patch application. The study medication will be used for 4 weeks. VAS (visual analog scale), BPI Q9 (quality of life) and global assessment have been used to assess the effectiveness. VAS will be assessed every week. BPI Q9 will be assessed at week 1 and week 4. Global assessment will be assessed at week 4. The safety of the study drug will be evaluated using adverse event (AE) report.

The investigator will assess the pain intensity of patients and increase or even decrease Fentanyl dosage every week. Fentanyl will be started on 25 or 50 ug per hr depending on investigator's judgement. Fentanyl will be administered for 4 weeks.

Inclusion Criteria:

• Patients have the history of head and neck tumor
• Patients who are proceeding radiotherapy
• Patients who are administered weak opioids and pain score (Visual analog scale) of 4

Exclusion Criteria:

• Patients who have been administered Fentanyl for pain treatment within 2 weeks before the study
• Patients who will have surgery within 1 month
• Known presence of distant metastasis