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Introduction: Irradiation of loaded tumor with high-Z nanoparticles with low energy photon of 192Ir source during brachytherapy increases absorbed dose of tumor due to increase in possibility of photoelectric phenomena. Therefore, this study aimed to investigate dose enhancement due to nanoparticles (NPs) with different atomic numbers and concentrations as well as effect of NPs distribution (uniform & non- uniform) on dose enhancement. Methods: Dosimetric parameters of HDR-192Ir source (MicroSelectron model) were calculated by MCNP-4C code on the basis of recommendations of AAPM, TG-43. A tumor (1 cm3) loaded with uniform and non-uniform distribution of 7, 18 and 30 mgr/gr of 79Au, 64Gd, 26Fe and 22Ti in water phantom (30×30×30 cm3) was simulated. Results: DEF of 4.7% to 19.4% and 3.3 to 18.6% were calculated respectively for uniform distribution of 79Au and 64Gd with 7 to 30 mgr/gr concentrations. For non-uniform distribution these values were 0.4%to 1.9% and 0.2% to 1.2%, respectively. Increased dose of the peripheral-health tissue due to presence of 2 to 8.5 mgr/gr of 79Au and 64Gd was estimated from 1.3% to 6.5% and 1.1% to 4.2%, respectively. Conclusion: increase of atomic number and concentrations of NPs enhance the absorbed dose due to increased possibility of photoelectric phenomena. Non-uniform distribution of NPs underestimated dose compared to uniform distribution therefore, considering accurate NPs distribution inside the tumor volume is crucial to calculation of dose enhancement. Targeted labeling of NPs for the maximum absorption by tumor and for the minimal penetration into peripheral tissues has potential to increase radiation therapeutic ratio.

Keywords: Brachytherapy; Dose Enhancement; Monte Carlo Simulation; Nanoparticles Distribution Function

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