Author: Clara Ferreira, Tomas Agustin Montenegro, Courtney C. Oare 👨🔬
Affiliation: University of Minnesota 🌍
Purpose: This work provides a simulated proof of concept for the use of intravitreal gold nanoparticle (AuNP) during eye plaque brachytherapy as a radiation shield to critical structures in the eye using MCNP.
Methods: Half-value layers (HVL) for different AuNP concentrations in water were generated using MCNP6.2 for I-125 and Pd-103. Homogenous mixtures versus modeling the AuNP as a lattice were also compared. A simplified eye model with a 16mm basal diameter and 5mm apex height tumor at the base and 20mm COMS eye plaque was generated in MCNP6.2. Simulations were conducted with different concentrations of AuNP modeled as a mixture within the vitreous for both I-125 and Pd-103. Track length estimator tallies were used to score dose to water at points representative of critical structures within the eye. Doses were normalized to provide 85Gy to the tumor apex.
Results: Concentrations of 30 mg/mL AuNP added to water reduced the HVL for I-125 from 16.7mm to 5mm and HVL for Pd-103 from 9.1mm to 2.4mm. In the simplified eye model using a concentration of 5 mg/mL within the vitreous, the dose to the optic disc dropped 14% and 24% for I-125 and Pd-103 respectively while maintaining 85 Gy to the tumor apex. At 30 mg/mL concentrations the dose reduction to the optic disc increased to 61% and 84% for I-125 and Pd-103.
Conclusion: These simplified models demonstrated the potential for intravitreal AuNP to be used as a shielding material during eye plaque brachytherapy. Compared to I-125, Pd-103 proved to have more synergy with this shielding method likely due to its lower average energy increasing the rate of photoelectric absorption. More work must be done to study the time dependent distribution of AuNP and the range of tumor sizes and positions in which this method is practical.