Currently, the well-studied mechanisms of improving radiosensitivity are to increase the primary DNA damage induced by radiotherapy and inhibit the repair ability of sub-lethal and lethal damages of tumor cells, and the most important lethal DNA damage is DNA double strand break, which further actives DNA-PKcs, KU70 and KU80 to complete DNA damage repair [34]. The gene discussed is XRCC5; the disease is neoplasm.