Radiotherapy has been an integral treatment modality for cancer. The field arose from and progressed through innovations in physics, engineering, and biology. The evolution of radiation oncology will rely on the continued adoption of advances from other fields. A new area of science that possesses the ability to impact radiation oncology is nanomedicine. Materials on the nanoscale provide many unique properties such as enhanced permeability and retention effect and superparamagnetism that are well suited for applications in radiation oncology. In this review, we will provide a comprehensive summary on how nanotechnology can improve cancer radiotherapy in aspects of treatment delivery and monitoring as well as diagnosis.