High-Z nanoparticles can increase the absorbed radiation dose if they are accumulated in tumor cells. The quantitative measure of this radiosensitization effect is the dose enhancement factor (DEF), that is, the ratio of the doses absorbed in the presence and in the absence of nanoparticles. In the present work, the values of the dose enhancement factors of Ta2O5, HfO2, and CeO2 ceramic nanoparticles were calculated analytically for monochromatic radiation of the X-ray energy range (1–180 keV) and for low-energy sources for brachytherapy: 103Pd (mean energy, 20.6 keV), 125I (26.7 keV), and 131Cs (30.4 keV). For all types of nanoparticles in the concentration of 5 mg/mL, the values of the dose enhancement factor were high both for monochromatic radiation and for brachytherapy sources. The highest DEF values of ~1.7 were obtained for nanoparticles of tantalum oxide. For brachytherapy sources, the highest dose enhancement factors (1.48 to 1.67) were obtained for Ta2O5 and HfO2 nanoparticles. These results confirm that ceramic nanoparticles are promising dose modifying agents for radiotherapy.