Computer aided design of a polarised source for in vivo X-ray fluorescence analysis.

A system has been developed which uses Monte Carlo computer simulations to aid the design and optimisation of a polarised source for in vivo X-ray fluorescence (XRF) analysis of heavy metals: The system is based on a version of the Monte Carlo code EGS4 which includes polarised photon interactions, running on a personal computer. The code was used to construct a model of a clinical polarised XRF system (based on a 300 kV therapy X-ray source) under development at Swansea for the measurement of Pt-based chemotherapy drugs in head and neck tumours. Several simulations were performed to investigate the variation of XRF measurement sensitivity with the material composition and geometry of the system components. Pt XRF spectra generated by the model were found to be in good agreement with experimental data. The optimum operating voltage for the system, predicted by the simulations and confirmed by experiment, was approx. 200 kV. The accuracy of the results obtained to date indicates that this technique will greatly facilitate future design and optimisation studies of a wide variety of XRF systems.