Nanoparticles can be used to increase the effects of hadrontherapy exactly where they are needed: in the cancer cells. This is so, because they can be coated with organic molecules which selectively target the cancer cells, going into them in much larger proportion than in the healthy cells. Then, when the body is irradiated with an ion beam, the interaction between the beam and the nanoparticles can produce an increase in the number of secondary species (electrons and free radicals) which damage the cell genetic material, increasing the cancer cell-killing ability of the treatment.
Among the materials which are being investigated for these radioenhancing nanoparticles, cerium oxides (ceria) are one of the most promising. It has been tested experimentally that ceria nanoparticles can, on the one hand, radiosensitise cancer cells while, on the other hand, radioprotect healthy cells.
To understand these complex radiosensitisation and radioprotection mechanisms is very challenging, but it is clear that a first step in this direction is to understand how charged particles (particularly electrons, which are abundantly produced by radiation) interact elastically and, mainly, inelastically with cerium oxides.
In our recent publication in the journal Physical Chemistry Chemical Physics, we have investigated from first principles the electronic excitation spectrum of both phases of ceria (CeO2 and Ce2O3), i.e., its Energy-Loss Function (ELF), by means of linear-response time-dependent density functional theory (TDDFT) calculations. For CeO2, material for which there are optical measurements, we found excellent agreement with experiment when local field effects are included in the calculations, while we also predicted the ELF of the more unknown Ce2O3.
These ELFs have been used to obtain the inelastic scattering probabilities of electrons in these materials, which, together with elastic scattering probabilities from the Mott theory, have provided the input for precise Monte Carlo simulations of the electron transport in ceria. These simulations have been used to try to reproduce the reflection electron energy loss spectrum experimentally determined for ceria (REELS, a very well-known electron analysis and spectroscopic technique). We found that the REELS spectrum can be fairly well reproduced by simulations which, moreover, allow interpreting the origin of the different features of the spectrum, which come from different electronic excitations of both CeO2 and Ce2O3. As it was suspected in the experimental work, the ceria material commonly used turns out to be a mix of these two phases of cerium oxide.
We expect that these calculations and simulations will help in the future to understand the physical mechanisms of ceria nanoparticle radiosensitisation in hadrontherapy.
The open access article, which has been showcased on the PCCP back cover, can be downloaded, free of charge, in the following link:
or through the Publications tab.
Image reproduced by permission of the authors from Phys. Chem. Chem. Phys., 2021, 23, 19173, DOI: 10.1039/D1CP01810H