Nearly 11 million people are diagnosed with cancer each year, and approximately half of these will undergo radiation therapy with photons, fast electrons, X-rays, gamma rays, protons or neutrons. Although there have been many advances in the accuracy of delivery of radiation to a tumor, this remains a challenge, as malignant tumors do not have well-defined borders and are often surrounded by radiosensitive structures or cells. This project will synthesize ultrasmall, water-soluble LaF3:Ce nanoparticles and conjugate to a cancertargeting molecule and a photosensitizer. In addition, the project will quantify reactive oxygen species (ROS) from each conjugate upon visible and Xirradiation, quantify the cytotoxicity of the conjugates to selected cancer cells in culture using an Xray therapeutic protocol, and determine the enhancement of the X-ray dose in the presence of the particles. Confirming these findings would lead to new clinical avenues for this treatment of refractory cancers.