Determination of the dose enhancement exclusively in tumor tissue due to the presence of GNPs.

Purpose: The purpose of this study is to investigate the differences between obtained percentage dose enhancements in areas around nanoparticles in GNPs (gold nanoparticles) enriched medium and percentage dose enhancements in the entire GNPs enriched medium including nanoparticles region.
Methods and Materials: To verify the accuracy of Ir-192 source simulation, the obtained values of air kerma strength, dose rate constants, and radial dose functions were compared against previously published results. Then a 1 cm × 1 cm× 1 cm tumor volume loaded with different diameters of GNPs were considered at a source to the tumor center of 1 cm. Finally, dose enhancements were obtained for 50, 100 and 200 nm GNPs as a function of various concentrations of the radiosensitizer and depth in phantom.
Results: Calculations showed that dose enhancement could be customized by varying the size of nanoparticles, concentrations and radial distance from the source. The highest PDE _GNP (The ratio of the increased deposited dose in the tumor region to the dose deposition in the no nano gold-containing structure) was acquired by 50 nm nanoparticles, 30 mg/g concentrations and in the highest distance from the source. (PDE _GNP ) and (PDE _around-GNP ) due to the presence of 7-30 mg/g concentration of GNPs ranged from 3-18.19% and 3.45-21.13%, respectively. The results of this study revealed that the correlation is significant at the 0.01 level and there is a non-negligible difference (up to 3%) between (D _around-GNP )and (D _GNP ).
Conclusion: By considering exclusively determination of dose enhancement in the just tumor tissue, calculating (D _around-GNP ) Instead of D _GNP may be a strategy for clinical use of nanoparticles in the radiation therapy. The results showed that with the increasing trend of dose enhancement in the GNPs loaded-tumor, dose enhancement decreases with an increase in the size of GNPs.
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