ABSTRACT
Purpose: Nowadays, cancer is one of the most important causes of morbidity and mortality in the world. The ideal aim of radiotherapy is delivering a lethal radiation dose to tumor cells while minimizing radiation exposure to healthy tissues around the tumor. One way to increase the dose in the tumor cells is the use of high-atomic number nanoparticles as radiosensitizer agents in these cells. The aim of this in vitro study was investigating the radiosensitization enhancement potential of the dextran-coated iron oxide nanoparticles (IONPs) on HeLa and MCF-7 cell lines in irradiations with high-energy electron beams. Materials and Methods: In this in vitro study, the cytotoxicity level of dextran-coated IONPs at different concentrations (10, 40, and 80 μg/ml) was assessed on HeLa and MCF-7 cell lines. To evaluate the radiosensitivity effect, the nanoparticles were incubated with the cells at different concentrations for 24 h and afterward irradiated with different doses (0, 2, 4, 6, and 8 Gy) of 6 and 12 MeV electron beams. The cells survival fractions were obtained by the methylthiazoletetrazolium assay. Results: Toxicity results of the nanoparticles at 10 and 40 μg/ml concentrations showed no significant cytotoxicity effect. The cells survival rates in groups receiving radiation in the absence and presence of IONPs showed a significant difference. The radiosensitivity enhancement induced by the nanoparticles in MCF-7 cell line was more than it in HeLa cell line. The average of radiosensitization enhancement factor at 10, 40, and 80 μg/ml concentrations and under 6 MeV irradiations obtained as 1.13, 1.19, 1.25, and 1.26, 1.28, 1.29 for HeLa, and MCF-7 cells, respectively. When 12 MeV electron beams were carried out, the values of 1.17, 1.26, 1.32, and 1.29, 1.32, 1.35 were obtained for the cells at the mentioned concentrations, respectively. Furthermore, the significant differences were observed in radiosensitization enhancement between 6 and 12 MeV electron beams irradiations. Conclusion: Use of dextran-coated IONPs can increase radiosensitivity and consequently at a given absorbed dose more cell killing will occur in cancerous cells. In other words, these nanoparticles can improve the efficiency of electron therapy
ABSTRACT
One of the intensity modulated radiation therapy [IMRT] methods is based on using compensators. The most important factor in designing a compensator is the accurate calculation of its thickness to achieve the intensity modulation of interest. To achieve that, the exact attenuation coefficient of compensator materials must be calculated. However, there are several parameters that are effective in calculating the attenuation coefficient of compensator materials. In this research, the effects of dosimeter and phantom type as well as irradiation dose and measurement depth in the calculation of this compensator characteristic were assessed. Using two types of dosimeters [RK and FC65G] and phantoms [RFA300plus and SP34], the effects of radiation dose and measured depth on the estimation of the effective attenuation coefficient was investigated for a 6MV linear accelerator. The value of applied radiation dose was 100, 200, 300 and 400 cGy, and the measured depths were 2, 5, 10, 15 and 20 cm. The measurements were carried out at the reference field size [10x10 cm[2]] and for a thickness of 1 cm of the compensator. The results indicated that radiation dose has no significant effect in calculating the effective attenuation coefficient of compensator materials. However, altering measured depth from 2 to 20 cm resulted in a change of more than 5% in the calculations. In addition, the type of the dosimeter and phantom used in this study had no significant effect on the calculations. Based on these findings, it is recommended that for more accurate estimation of the effective attenuation coefficient of a compensator material, it is necessary to measure the attenuation coefficient at different depths of the treatment field