SUMMARY

Gold nanoparticles can serve as an ideal radiosensitizer for radiation therapy due to the high-atomic-number nature of gold and the increased tumor specificity in nanoparticle form. The degree of radiosensitization is highly dependent on both the local gold nanoparticle concentration in the tumor and the radiation source type. Previous Monte Carlo simulations have demonstrated that the gamma-ray energy spectrum of Ytterbium-169 is a strong candidate for a high dose rate brachytherapy implementation of gold nanoparticle-aided radiation therapy. Therefore, the current study focuses on the design of a high dose rate Ytterbium-169 source that would maximize dose enhancement during gold nanoparticle-aided radiation therapy; while meeting the practical constraints for the production of a clinically relevant brachytherapy source. Different encapsulation materials are studied in order to determine its effect on the dosimetric characteristics of the source. Specifically, the photon spectra, secondary electron spectra, and dose enhancement characteristics are calculated via Monte Carlo simulations to elucidate the effects on potential radiosensitization during gold nanoparticle-aided radiation therapy. Furthermore, this project involves a study into the modification of external x-ray beams from a Philips RT-250 orthovoltage x-ray machine in an attempt to match the dosimetric characteristics of the Ytterbium-169 brachytherapy source. This investigation will enable the production of an external beam that can serve as a good surrogate of an actual brachytherapy source and facilitate the pre-clinical investigation of gold nanoparticle- aided radiation therapy with Ytterbium-169.