Radiotherapy is an invaluable tool in cancer treatment. However, as modalities get ever more complex, it becomes increasingly evident that radiotherapy is a double-sided sword that must be yielded with care to assure as much damage to the tumor while sparing healthy tissue as possible. My project is to develop materials that can visualize in three dimensions where and how much radiation was given. Particularly, I synthesize nanoparticles and try to optimize their ability to store a fraction of the energy deposited during irradiation that can be read out later as a measure of the dose. Armed with such a device, medical physicists can directly compare their expected treatment plan with the real deal, catching unforeseen errors before treating patients. With confidence gained in these plans, it is possible to target cancer tumors more directly than anyone has ever dared before.