Investigating Methods of Normalization for X-ray Fluorescence Measurements of Zinc in Nail Clippings Using the Topas Monte Carlo Code

Development of portable X-ray fluorescence devices has made it easier to quickly assess trace elements such as zinc in human tissue. Zinc deficiency can have serious implications for growth and development of the human body. From recent studies, zinc content in nail clippings has been suggested to be an effective biomarker for zinc status. In this study, a Monte Carlo simulation approach was used to investigate the use of a portable X-ray fluorescence system for detecting zinc in nail clippings. The portable X-ray device was modelled using specifications from the manufacturer input to the TOPAS Monte Carlo code (Geant4 simulation software). The simulations were carried out for varying nail clipping thickness (0.3 mm – 1.2 mm) as clipping thickness has previously been shown to influence zinc signal in experimental trials. Each simulation was run for 10 histories and the statistical uncertainty was less than 3.5%. The obtained energy spectra from different measurements were analyzed and three different normalization techniques (coherent, Compton, and entire spectrum) were introduced. General agreement between simulation and experimental trends were observed, indicating successful benchmarking of the simulation design. All three normalization techniques showed a slightly negative trend for signal with respect to clipping thickness, consistent with experimental results. The simulation results suggested that coherent normalization can be a particularly robust normalization procedure, showing a small relative variation in signal over a wide range of clipping thickness.