Nanoparticle (NP) assisted magnetic hyperthermia (NMH) is a clinically proven method for cancer treatment. High-Z magnetic NPs could also be a perspective object for combining hyperthermia with tumor radiosensitization. However, this application of NPs is little studied, and it is unclear as to what particle compositions one can rely on. Therefore, the present work focuses on the search of materials that combine alternating magnetic field induced heating and high atomic number related dose enhancement abilities. A theoretical evaluation of 24 promising NP compositions was performed: the values of dose enhancement factor (DEF) were determined for kilovoltage x-ray spectra (30–300 kVp), as well as specific absorption rate (SAR) values were calculated for various combinations of elemental compositions and particle size distributions. For the alternating magnetic fields with amplitude $75\text{–}200\mathrm{Oe}$ and frequency $100\mathrm{kHz}$ , the maximum obtained SAR values ranged from 0.35 to $6000\mathrm{W}{\mathrm{g}}^{-1}$ , while DEF values for studied compounds ranged from 1.07 to 1.59. The increase in the monodispersity of NPs led to a higher SAR, confirming well-known experimental data. The four types of SAR dependences on external magnetic field amplitude and anisotropy constant were found for various particle sizes. The most predictable SAR behavior corresponds to larger NPs (∼70–100 nm). Thus, based on these calculations, the most promising for the combination of NMH with radiotherapy, from a physical point of view, are $\mathrm{L}{\mathrm{a}}_{0.75}\mathrm{S}{\mathrm{r}}_{0.25}\mathrm{Mn}{\mathrm{O}}_3$ , $\mathrm{G}{\mathrm{d}}_5\mathrm{S}{\mathrm{i}}_4$ , $\mathrm{SmC}{\mathrm{o}}_5$ , and $\mathrm{F}{\mathrm{e}}_{50}\mathrm{R}{\mathrm{h}}_{50}$ . The greatest dose enhancement is expected for superficial radiotherapy (in the voltage range up to ∼60 kVp).

Nanoparticles (NPs) with a high atomic number (Z) are promising radiosensitizers for cancer therapy. However, the dependence of their efficacy on irradiation conditions is still unclear. In the present work, 11 different metal and metal oxide NPs (from Cu (Z_Cu = 29) to Bi₂O₃ (Z_Bi = 83)) were studied in terms of their ability to enhance the absorbed dose in combination with 237 X-ray spectra generated at a 30–300 kVp voltage using various filtration systems and anode materials. Among the studied high-Z NP materials, gold was the absolute leader by a dose enhancement factor (DEF; up to 2.51), while HfO₂ and Ta₂O₅ were the most versatile because of the largest high-DEF region in coordinates U (voltage) and E_eff (effective energy). Several impacts of the X-ray spectral composition have been noted, as follows: (1) there are radiation sources that correspond to extremely low DEFs for all of the studied NPs, (2) NPs with a lower Z in some cases can equal or overcome by the DEF value the high-Z NPs, and (3) the change in the X-ray spectrum caused by a beam passing through the matter can significantly affect the DEF. All of these findings indicate the important role of carefully planning radiation exposure in the presence of high-Z NPs.

Surface modifications of radiosensitizing gold nanoparticles (GNP), in particular coating with polyethylene glycol (PEG), may greatly improve their physico-chemical, pharmacological and theranostic properties. However, GNP coating material can seriously alter the efficacy of radiosensitization. We performed a Monte-Carlo simulation of 17 nm GNP PEGylation (8.5 nm layer thickness) effects on secondary radiation spectra at different energies of primary photons (from ∼8 keV to 1 MeV). Our calculations revealed a decrease of the amount of low energy electrons (LEE) that leave PEGylated GNP (from 20% to 40% at the photon energy <500 keV, and from 20% to 0% at energies 500–1000 keV). In all cases, the average energy of the low-energy component of the electron spectrum was smaller for coated GNP. Total energy differed only slightly at photon energy up to ∼200 keV; at bigger energies the normalized total energy of secondary electrons that left the PEG shell significantly (∼20%) exceeded the respective value for electrons that left the uncoated GNP. Thus, rational design of GNP-based radiosensitizers should include critical assessment of physico-chemical properties of the material used for surface modification.