Quantifying Macroscopic and Microscopic Radiation Dose Enhancement with Gold Nanoparticles for a Range of Therapeutic Energies

The purpose of this study is to computationally quantify the macroscopic and microscopic radiation dose enhancement effects of different sizes and shapes of gold nanoparticles. A MicroSelectron HDR Ir-192 brachytherapy seed and a Varian 600C gantry head with 6 MV and 18 MV photon energies were modeled using Monte Carlo N-Particle radiation transport software (MCNP 6.2, Los Alamos National Laboratory). The repeating structures capability of MCNP6.2 was utilized to simulate nanoparticles of varying sizes inside a tumor with a diameter of 1 x 1 x 1 cm³. Additionally, a phase space file was created to compute dose deposited from secondary electrons around single nanoparticles of varying shapes (nanocubes, nanoprisms and nanospheres). Macroscopic simulations show an increase in dose enhancement generally with increasing mass percentage of gold and compare well with experimental results. Microscopic simulations show an increased dose enhancement of 20% - 50% due to secondary electrons up to 1 µm from the nanoparticle and is highest for nanoprisms due to a larger surface area to volume ratio. This work indicates the potential for gold nanoparticles to provide significant dose enhancement and more effective tumor cell killing in radiation oncology practice.