Monte Carlo modeling of gold nanoparticles detection limits of benchtop three-dimensional L- and K-shell X-ray fluorescence mapping systems

This study aims to investigate the detection limits of gold nanoparticle (GNP) concentrations by Monte Carlo (MC) modeling of benchtop polychromatic K- and L-shell X-ray fluorescence mapping system. In Monte Carlo N-Particle (MCNP version 6.1) simulations, a 0.25-cm-diameter cylinder containing GNPs of various concentrations (i.e., 0.005%–1.0% gold by weight, wt%) was assumed to be located at the center of a cylindrical water phantom of various diameters (1.0–10 cm). Two different sets of incident pencil beam X-rays and detectors were modeled to stimulate X-ray fluorescence (XRF) of GNPs: (1) 62 kVp and silicon drift detector for L-XRF, (2) 105 kVp and cadmium telluride detector for K-XRF. The detection limits were calculated for given radiation doses to the center of phantom (375–1500 mGy). When the diameter of the phantom was 1 cm, the detection limits for L-XRF and K-XRF were an order of 0.001 wt% and of 0.01 wt%, respectively. The detectability of K-XRF turned out to be superior to that of L-XRF for the phantoms greater than or equal to 3 cm in diameter. The MC results will provide a guide for developing an optimal benchtop XRF imaging system for in vivo preclinical imaging, depending on the sizes of GNP-loaded objects, GNP concentrations, and radiation doses.