Monte Carlo Evaluation of Dose Enhancement Using Gold Nanoparticles In 192ir Brachytherapy
Abstract
Purpose
This study aimed to determine the dose enhancement factor (DEF) in irradiations using a ¹⁹²Ir brachytherapy source in the presence of different mass concentrations of gold nanoparticles (AuNPs) homogeneously distributed within a tumor volume, through Monte Carlo simulations with the PENELOPE code.
Methods
A clinical ¹⁹²Ir brachytherapy source (Varian, GammaMed Plus model), widely employed in gynecological treatments, was modeled using Monte Carlo simulations with the PENELOPE code. The tumor was represented as a homogeneous spherical volume with a fixed radius of 4.0 cm and density equivalent to water. AuNPs were assumed to be homogeneously distributed throughout the tumor volume, with no volume displacement or localized high-density regions. Gold mass concentrations of 0.5%, 1.0%, 2.0%, 3.0%, 5.0%, and 100% (w/w) were evaluated. For each concentration, the total AuNPs mass was calculated and converted into an equivalent volume of bulk gold, assuming a density of 19.32 g/cm³. The DEF was calculated as the ratio between absorbed dose in the presence and absence of gold at different depths, considering increased photoelectric interaction probability due to gold.
Results
A significant increase in absorbed dose was observed in the presence of gold for all concentrations, particularly at shallow depths near the source. The maximum DEF value, approximately 68%, was observed at 0.19 cm for the lowest gold concentration (0.5% w/w), while the minimum DEF, around 18%, occurred at 1.0 cm depth for the highest evaluated concentration (5.0% w/w). Overall, DEF values ranged from approximately 18% to 68%, depending on depth and gold concentration. Higher DEF values were observed at shallower depths, with a progressive reduction as the distance from the source increased, reflecting localized energy deposition from short-range secondary electrons.
Conclusion
The dose enhancement effect is strongly associated with photoelectric interactions, supporting the potential use of gold nanoparticles as dose-enhancing agents in brachytherapy optimization.