The Prospects of Metal Oxide Nanoradiosensitizers: The Effect of the Elemental Composition of Particles and Characteristics of Radiation Sources on Enhancement of the Adsorbed Dose

Nanoparticles with a high atomic number are of interest as radiosensitizers for radiation therapy of cancer. A variety of nanoparticles and radiation sources makes the challenge of selecting their optimal combinations to achieve maximum irradiation efficacy relevant. In this work, we calculated the values of the dose enhancement factors of elemental compositions of metal oxide nanoparticles (Al₂O₃, TiO₂, MnO₂, Fe₂O₃ and Fe₃O₄, NiO, GeO₂, ZrO₂, CeO₂, Gd₂O₃, Tm₂O₃, HfO₂, Ta₂O₅, and Bi₂O₃), as well as GeO₂ and HfO₂ doped with the rare-earth elements lanthanum or ytterbium in combination with monochromatic photons (1–500 keV) and X-ray radiation corresponding to the radiation of kilovoltage X-ray therapy machines. At a nanoparticle concentration of 10 mg/mL, the maximum values of the dose enhancement factors were from 1.03 to 2.55 for monochromatic radiation and from 1.01 to 2.33 for the studied X-ray spectra. Doping GeO₂ with 20% lanthanum or ytterbium led to an increase in the maximum value of dose enhancement factors by ~10%. Doping HfO₂ did not lead to significant changes in the value of dose-enhancement factors. Thus, all studied elemental compositions of nanoparticles, with the exception of Al₂O₃ (a dose enhancement factor ~1.02), are promising for application in kilovoltage X-ray radiotherapy. At the same time, the complex dependence of dose enhancement factors on the spectral composition of X-ray radiation requires detailed studies of the impact of irradiation conditions on the magnitude of the radiomodifying effect of nanoparticles.