Radiotherapy　(RT)　is　an　effective　and　widely　applied　cancer　treatment　strategy　in　clinic.　However,　it　usually　suffers　from　radioresistance　of　tumor　cells　and　severs　side　effects　of　excessive　radiation　dose.　Therefore,　it　is　highly　significant　to　improve　radiotherapeutic　performance　and　monitor　real-time　tumor　response,　achieving　precise　and　safe　RT.　Herein,　an　X-ray　responsive　radio-pharmaceutical　molecule　containing　chemical　radiosensitizers　of　diselenide　and　nitroimidazole　(BBT-IR/Se-MN)　is　reported.　BBT-IR/Se-MN　exhibits　enhanced　radiotherapeutic　effect　via　a　multifaceted　mechanisms　and　self-monitoring　ROS　levels　in　tumors　during　RT.　Under　X-ray　irradiation,　the　diselenide　produces　high　levels　of　ROS,　leading　to　enhanced　DNA　damage　of　cancer　cell.　Afterwards,　the　nitroimidazole　in　the　molecule　inhibits　the　damaged　DNA　repair,　offering　a　synergetic　radiosensitization　effect　of　cancer.　Moreover,　the　probe　shows　low　and　high　NIR-II　fluorescence　ratios　in　the　absence　and　presence　of　ROS,　which　is　suitable　for　precise　and　quantitative　monitoring　of　ROS　during　sensitized　RT.　The　integrated　system　is　successfully　applied　for　radiosensitization　and　the　early　prediction　of　in　vitro　and　in　vivo　RT　efficacy.