We are investigating the use of high atomic number (Z) nanoparticles as vascular-disrupting agents, when combined with radiation. High-Z materials are attractive for this project due to the relatively high photoelectric cross-section. By specifically targeting the endothelial cells of the tumor vasculature, we anticipate a larger effect than by attempting to distribute the nanoparticles throughout the tumor volume. Our concept should be effective for both low energy (brachytherapy) and high energy (MV) clinical scenarios.