Synthesis and evaluation of thermoluminescence properties of ZrO2:Mg for radiotherapy dosimetry.

This study aimed to investigate the thermoluminescent properties of ZrO2:Mg irradiated with a 6 MV X-ray beam and its potential application in radiotherapy dosimetry. ZrO2 powder was synthesized using the sol-gel method and Mg was used as a dopant. Irradiations were performed with ZrO2:Mg chips located at the center of a 10 × 10 cm2 radiation field at a source surface distance of 100 cm, below a stack of solid water slabs, at the depth of maximum absorbed dose. The investigated characteristics of the material included linearity with radiation dose, reproducibility, accuracy, sensitivity and fading. Regarding the intrinsic difference of the samples, the glow curves of the investigated ZrO2:Mg chips exposed to 1 Gy of 6 MV X-rays exhibited three or four peaks. The ZrO2:Mg samples showed a 47% fading at 24 h after irradiation, and the reproducibility of the thermoluminescence reading of ZrO2:Mg for equal irradiation conditions was ± 21%. The thermoluminescence response of the investigated ZrO2:Mg samples to various absorbed doses from 0.5 to 2.5 Gy showed a gentle increase of the thermoluminescence intensity with increasing absorbed dose. The obtained results show that ZrO2:Mg is not an appropriate candidate for X-ray photons in radiotherapy, due to low thermoluminescence peak temperature, low reproducibility, low sensitivity to various absorbed doses and significant fading.

Enhanced cytotoxic and genotoxic effects of gadolinium-doped ZnO nanoparticles on irradiated lung cancer cells at megavoltage radiation energies.

The purpose of this study was to investigate the radiation dose enhancement effects of gadolinium-doped zinc oxide nanoparticles (Gd-doped ZnO NPs) under the megavoltage (MV) X-ray irradiation. ZnO NPs have preferred photocatalytic properties under UV light for cancer killing. UV light has limited applications in cancer treatment and it is necessary to use X-ray photons with MV energies. In order to increase the absorption of radiation and also to enhance the imaging visualization capabilities of ZnO NPs, gadolinium (Gd) as a high atomic number element was selected for doping into the structure of ZnO NPs. Gd-doped ZnO NPs were synthesized by a chemical precipitation method and characterized by transmission electron microscopy, powder X-ray diffraction, ultraviolet-visible spectroscopy, and energy-dispersive X-ray techniques. Cellular uptake was assessed by TEM and inductively coupled plasma mass spectrometry. NPs cytotoxicity was analyzed by MTT assay and radiation dose enhancement was measured by clonogenic survival assay. Apoptosis induction, cell cycle progression, micronucleus formation and expression of DNA double-strand break repair genes of XRCC2 and XRCC4 were determined by flow cytometry, micronucleus assay, and quantitative real-time polymerase chain reaction. CT and MR imaging were used to analyze the image visualization capabilities of NPs. NPs characterization showed that highly pure crystalline Gd-doped ZnO NPs with a narrow size distribution and grain size of 9 nm were synthesized. Gd-doped ZnO NPs were distributed in the cells and showed dose-dependent toxicity. Combination of Gd-doped ZnO NPs with 6 MV X-rays induced dose-dependent radiosensitivity with sensitizer enhancement ratios (SER) of 1.47 and 1.61 for 10 and 20 µg/mL NPs concentrations. Cancer cells blocked in G1, apoptosis rates, and micronuclei formation was enhanced and inversely, the DNA repair efficiency was impaired by down regulation of the mRNA levels of XRCC2 and XRCC4 genes. Gd-doped ZnO NPs enhanced the contrasts of CT and MR images of cancer cells. Overall, the results of this study provide detailed biological insights on the dose enhancement of Gd-doped ZnO NPs at MV radiations, which would contribute to the further development of this potent theranostic platform for clinical applications.

Enhancement of radiosensitivity of melanoma cells by pegylated gold nanoparticles under irradiation of megavoltage electrons.

PURPOSE: Gold nanoparticles (GNP) have significant potential as radiosensitizer agents due to their distinctive properties. Several studies have shown that the surface modification of nanoparticles with methyl polyethylene glycol (mPEG) can increase their biocompatibility. However, the present study investigated the radiosensitization effects of mPEG-coated GNP (mPEG-GNP) in B16F10 murine melanoma cells under irradiation of 6 MeV Electron beam. MATERIALS AND METHODS: The synthesized GNP were characterized by UV-Visible spectroscopy, dynamic light scattering, transmission electron microscopy, and zeta potential. Enhancement of radiosensitization was evaluated by the clonogenic assay at different radiation doses of megavoltage electron beams. RESULTS: It was observed that mPEG-GNP with a hydrodynamic size of approximately 50 nm are almost spherical and cellular uptake occurred at all concentrations. Both proliferation efficiency and survival fraction decreased with increasing mPEG-GNP concentration. Furthermore, significant GNP sensitization occurred with a maximum dose enhancement factor of 1.22 at a concentration of 30 µM. CONCLUSIONS: Pegylated-GNP are taken up by B16F10 cancer cells and cause radiosensitization in the presence of 6 MeV electrons. The radiosensitization effects of GNP may probably be due to biological processes. Therefore, the underlying biological mechanisms beyond the physical dose enhancement need to be further clarified.