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

X-ray fluorescence and energy dispersive x-ray diffraction for the quantification of elemental concentrations in breast tissue

This paper presents improvements on a previously reported method for the measurement of elements in breast tissue specimens (Geraki et al 2002 Phys. Med. Biol. 47 2327-39). A synchrotron-based system was used for the detection of the x-ray fluorescence (XRF) emitted from iron, copper, zinc and potassium in breast tissue specimens, healthy and cancerous. Calibration models resulting from the irradiation of standard aqueous solutions were used for the quantification of the elements. The present developments concentrate on increasing the convergence between the tissue samples and the calibration models, therefore improving accuracy. For this purpose the composition of the samples in terms of adipose and fibrous tissue was evaluated, using an energy dispersive x-ray diffraction (EDXRD) system. The relationships between the attenuation and scatter properties of the two tissue components and water were determined through Monte Carlo simulations. The results from the simulations and the EDXRD measurements allowed the XRF data from each specimen to be corrected according to its composition. The statistical analysis of the elemental concentrations of the different groups of specimens reveals that all four elements are found in elevated levels in the tumour specimens. The increase is less pronounced for iron and copper and most for potassium and zinc. Other observed features include the substantial degree of inhomogeneity of elemental distributions within the volume of the specimens, varying between 4% and 36% of the mean, depending on the element and the type of the sample. The accuracy of the technique, based on the measurement of a standard reference material, proved to be between 3% and 22% depending on the element, which presents only a marginal improvement (1%-3%) compared to the accuracy of the previously reported results. The measurement precision was between 1% and 9% while the calculated uncertainties on the final elemental concentrations ranged between 10% and 16%.

Anomalous Rayleigh scatter in dilute media

Anomalous Rayleigh scatter is examined for dilute concentrations of the biomedically relevant element iodine in aqueous media including measurements with monochromatic synchrotron radiation in the vicinity of the iodine K-edge. The measurements agree with anomalous scatter-factor corrections to the form-factor approximation which has been shown to have good agreement with higher precision S-matrix calculations for small angle scatter over a wide range of energies but has not been adequately tested at the edge. Monte Carlo modelling, including the modelling of polarized Compton and Rayleigh scattered x-rays, is used to determine the relative contributions of the scatter and fluorescent components at the detector as well as the modelling of self-absorption and relative dose in the determination of detection limits. A Rayleigh scatter minimum of 28 barns/sr was observed at an energy 10 +/- 5 eV below the K-edge of iodine at a position predicted from an evaluation of the dispersion integral that includes bound-bound resonance contributions. Minimum detectable concentrations for observation of the anomalous Rayleigh scatter feature at an exposure of 10 mSv, predicted for iodine and iron, are 1 mg ml(-1) and 10 mg ml(-1), respectively. Upper limits to detection of the feature imposed by degradation of the signal by self-absorption are 0.021 g cm(-2) and 0.0029 g cm(-2) radiation lengths, respectively.