Abstract: The present invention is directed to methods for the treatment of cancer with a combination of radiation, cerium oxide nanoparticles and at least one chemotherapeutic agent. Cerium oxide nanoparticles (CONPs) are nanometer-sized crystals of cerium oxide, typically ranging between about one nanometer to about 20 nanometers in longest dimension. The present methods use cerium oxide nanoparticles to enhance radiation-induced and chemotherapy-induced cancer cell death and also reduce the toxicity associated with radiation therapy and chemotherapy.