Evaluation of EDXRF configurations to improve the limit of detection and exposure for in vivo quantification of gadolinium in tumor tissue

Abstract

In this paper the configuration of an Energy Dispersive X-Ray Fluorescence (EDXRF) system optimized for in vivo quantification of gadolinium in tumor tissue was studied. The system was configured using XMI-MSIM software designed to predict the XRF spectral response using Monte Carlo simulations. The studied setup is comprised of an X-ray tube, tuned to different voltages, and a copper filter system configured with variable thickness, which emits a spectrally narrow beam centered on the specific excitation energy. The values for the central energy excitation and the spectral width were adjusted to optimize the system, using like figures of merit: minimization of the limit of detection, measurement uncertainty and radiation exposure. These values were obtained in two stages. The first was successive simulations of incident spectra with central energy in the range of 50-70keV. The second was comprised of simulations with incident spectra of different widths (8-29keV), all with the same determined central energy, evaluating the limit of detection depending on the exposure. This made it possible to find the best balance between system sensitivity and the delivered dose. The obtained results were compared with those produced by radioactive sources of 241Am whose activity was set to produce the same exposure as the proposed setup. To evaluate the feasibility of in vivo quantification, a set of tumor phantoms of 1-6cm3 at different depths and labeled with a gadolinium concentration of 250ppm was evaluated. From the resulting spectrum, calibration curves were obtained in function of the size and depth of the tumor, allowing for the evaluation of the potential of the methodology.