Monte Carlo methods for the in vivo analysis of cisplatin using X-ray fluorescence

A Monte Carlo method has been used to model the measurement of cisplatin uptake with in vivo X-ray fluorescence. A user-code has been written for the EGS4 Monte Carlo system that incorporates linear polarisation and multiple element fluorescence extensions. The yield of fluorescent photons to the mainly Compton scattered background is computed for our detector arrangement. The detector consists of a mutually orthogonal arrangement of X-ray tube, aluminium polariser and high purity germanium scintillation detector. The influence of tube voltage on the minimum detectable concentration is modelled for 100 through 150 kVp X-radiation. The code is able to predict absorbed dose to the patient which will influence the optimal choice of tube voltage. The influence of alterations to collimator design and scatterer construction can also be examined. A minimum detectable concentration of 50 ppm is determined from measurements with a 115 kVp X-ray source and a 615 ppm cisplatin sample in a water phantom.