MnSe@Bi2Se3 core-shell nanostructures with highly integrated imaging and therapy functions are fabricated by a simple cation exchange method. Using those nanoparticles as a theranostic agent, a promise concept is further demonstrated to enhance conventional radiotherapy by: i) using X-ray absorbing agents to locally concentrate radiation energy and ii) employing near-infrared-light-triggered photothermal therapy to overcome hypoxia-associated radioresistance.