Optimal energy fluorescence sources for in vivo x-ray fluorescence measurements of bone strontium

The choice of an optimum energy fluorescence source for in vivo x-ray fluorescence (XRF) can be challenging. This article describes a Monte Carlo study that systematically investigates possible sources for the in vivo XRF measurement of strontium in bone, with the ultimate goal of improving current measurement systems. A benchmarked EGS5 model was used to test source energies ranging from 17.2 keV to 21.7 keV to determine which source energies maximized the strontium XRF signal. A systematic search was then conducted to find potential radioisotope sources in the optimal energy range and simulations were performed of each source. The overall conclusion is that ¹⁰³Pd is a promising alternative to the ¹⁰⁹Cd and ¹²⁵I radioisotope sources used in prior systems. Monte Carlo studies suggest, however, that best performance could be obtained using a portable XRF gun with a rhodium target, although this would deliver a higher radiation dose.