“…Prognostic value of radiosensitivity associated with better local control has been suggested for some head and neck cancers excluding NPC 3–6 . Regression of tumor during or shortly after curative radiation therapy has been suggested to provide an in vivo indication of tumor radiosensitivity 6,7 . However, the volume by which a tumor changes after irradiation depends on multiple factors such as the percentage of cancer cells killed, the mode of cell death, the architecture of the tumor, the amount of radiation induced surrounding tissue changes, including inflammation and/or necrosis, and the efficiency of clearance of dead cells from the diseased area.…”