Asghar Mesbahi

Background. Nanoparticle-based radiation therapy using metal nanoparticles is an adjuvant therapy that makes tumor cells more sensitive to radiation. In this study, we have used plasmid to study the effect of radiation dose rate on the amount of radiation sensitization of bismuth oxide nanoparticles. Methods. In this study, bismuth oxide nanoparticles coated with polyethylene glycol were used as megavoltage radiation sensitizers. In this research, we used DNA plasmid PCEP4-102 as a nanoscopic dosimetry probe to measure the radiation sensitization effect of metal nanoparticles in radiation therapy. Plasmid samples with and without coated nanoparticles were irradiated with 6 megavolt X-rays at dose rates of 50 MU/min and 833 MU/min. Results. The dose enhancement factor for plasmid samples containing Bi2O3 nanoparticles irradiated with 6 megavolt X-rays was 1.33 ± 0.1. Increasing the dose rate from 50 MU/min to 833 MU/min did not cause any obvious change in the amount of plasmid damage in the plasmid samples without nanoparticles. Considering the plasmid samples containing metal nanoparticles, the values of the dose enhancement factor for the samples exposed to 6MV X-ray irradiation at a dose rate of 833 MU/min were significantly increased compared to the samples irradiated with 6 MV X-rays at a dose rate of 50 MU/min. Conclusion. This study confirms the efficiency of bismuth oxide nanoparticles in increasing the effectiveness of radiation therapy. In the presence of nanoparticles, increasing the dose rate can cause more damage to the plasmid by chemical and physicochemical enhancement in radiation therapy by megavolt photons. Practical Implications. The results of this study confirm the radiosensitization potential of metallic nanoparticles and show that increasing the dose rate leads to an increase in the damaging effect of nanoparticle-aided radiation therapy.

Nanoparticles (NPs) as radiosensitizers present a promising strategy for enhancing radiotherapy effectiveness, but their potential is significantly influenced by the properties of their surface coating, which can impact treatment outcomes. Most Monte Carlo studies have focused on metallic NPs without considering the impact of coating layers on radiosensitization. In this study, we aim to assess both the physical and radiobiological effects of nanoparticle coatings in nanoparticle-based radiation therapy. In this simulation study, we used Geant4 Monte Carlo (MC) toolkit (v10.07.p02) and simulated the bismuth, gold, iridium and gadolinium NPs coated with polyethylene glycol (PEG-400: Density: 1.13 g/cm³, Molar mass: 380–420 g/mol) as radiosensitizer for photon beams of 30, 60 and 100 keV. Secondary electron number and reactive oxygen species enhancement factor were estimated. Also, dose enhancement factor (DEF) was determined in spherical shells with logarithmic scale thickness from the nanoparticle surface to 4 mm. Secondary electron emission was highest at 30 keV for gold, bismuth, and iridium NPs, while gadolinium NPs peaked at 60 keV. Coating reduced electron emissions across all energies, with thicker coatings leading to a more significant decrease. DEF values declined with increasing radial distance from the NP surface and were lower with thicker coatings. For gadolinium NPs, DEF behavior differed due to K-edge energy effects. Reactive species generation varied, showing maximum production at 30 keV for gold, bismuth, and iridium NPs, while gadolinium NPs showed peak activity at 60 keV. PEG coatings enhanced reactive species formation at 100 keV. The findings indicate that the coating layer thickness and material not only influence the emission of secondary particles and DEF but also affect the generation of reactive species from water radiolysis. Specifically, thicker coatings reduce secondary particle emission and DEF, while PEG coatings demonstrate a dual behavior, offering both protective and enhancing effects depending on photon energy. These insights underscore the importance of optimizing NP design and coating in future studies to maximize therapeutic efficacy in nanoparticle-based radiation therapy.

To qualify for nuclear applications, materials must meet specific criteria, including mechanical properties, high-temperature behavior, corrosion resistance, and high-temperature oxidation resistance. High Entropy Alloys (HEAs) are particularly suitable for these applications due to their unique properties. Consequently, we conducted a theoretical and simulation-based approaches to assess some critical properties including radiation shielding properties of some quinary FeNiCoCr HEAs. In this study, we focused on quinary FeNiCoCr HEAs, whose corrosion properties have been previously examined in the literature. We investigated the thermodynamic and radiation shielding properties of HEAs with sixteen different compositions. Our methodology included evaluating thermodynamic parameters such as Mixing Entropy (∆S_mix) and Mixing Enthalpy (∆H_mix), as well as structural characteristics like Valence Electron Concentration (VEC) and Atomic Size Difference (δ). This allowed us to systematically deduce the phase behavior and stability of various HEAs. Through computational modeling, we assessed the radiation shielding capabilities of these alloys, particularly their effectiveness in attenuating gamma ray and fast neutrons. The results identified FeNiCoCrW as the alloy with the lowest fast neutron removal cross-section values, highlighting its potential for nuclear applications. Its high melting point and the synergistic interplay between its elemental composition and thermodynamic properties suggest broad applicability in extreme environments. Thus, FeNiCoCrW emerges as a promising HEA with multifunctional capabilities, warranting further exploration and potential integration into advanced engineering solutions.

In addition to specific dosimetric properties of protons, their higher biological effectiveness makes them superior to X-rays and gamma radiation, in radiation therapy. In recent years, enrichment of tumours with metallic nanoparticles as radiosensitizer agents has generated high interest, with several studies attempting to confirm the efficacy of nanoparticles in proton therapy. In the present study Geant4 Monte Carlo (MC) code was used to quantify the increased nanoscopic dose deposition of 50 nm metallic nanoparticles including gold, bismuth, iridium, and gadolinium in water upon exposure to 5, 25, and 50 MeV protons. Dose enhancement factors, radial dose distributions in nano-scale, as well as secondary electron and photon energy spectra were calculated for the studied nanoparticles and proton beams. The obtained results demonstrated that in the presence of metallic nanoparticles an increase in proton energy leads to a decrease in secondary electron and photon production yield. Additionally, an increase in the radial dose enhancement factor from 1.4 to 16 was calculated for the studied nanoparticles when the proton energy was increased from 5 to 50 MeV. It is concluded that the dosimetric advantages of proton beams could be improved significantly in the presence of metallic nanoparticles.

Nanoparticle-based composites have the potential to meet requirements for radiosensitization in both therapeutic and diagnostic applications. The radiosensitizing properties of nanoparticles could be reliant on the nature of their coating layer. Any gains in reduced toxicity and aggregation or improved delivery to tumor cells for coated nanoparticles must be weighed against the loss of dose enhancement. The radiosensitization potential of coated NPs is confirmed by numerous studies but in most of them, the coating layer is mostly applied to reduce toxicity of the NPs and for stability and biocompatibility aims. While the direct effects of the coating layer in radiosensitization—were ignored and not considered. This review provides an overview of double-edged impact of nanoparticle coating on the radiosensitization potential of nanostructures and discusses the challenges in choosing appropriate coating material in the aim of achieving improved radioenhancement. Coating layer could affect the radiosensitization processes and thereby the biological outcomes of nanoparticle-based radiation therapy. The physicochemical properties of the coating layer can be altered by the type of the coating material and its thickness. Under low-energy photon irradiation, the coating layer could act as a shield for nanoparticles capable of absorb produced low-energy electrons which are important levers for local and nanoscopic dose enhancement. Also, it seems that the coating layer could mostly affect the chemical process of ROS production rather than the physicochemical process. Based on the reviewed literature, for the irradiated coated nanoparticles, the cell survival and viability of cancer cells are decreased more than normal cells. Also, cell cycle arrest, inhibition of cell proliferation, DNA damage, cell death and apoptosis were shown to be affected by coated metallic nanoparticles under irradiation.