Determination of transmission curves of X-ray spectra for contrast-enhanced digital mammography using Monte Carlo simulations

Purpose: To determine transmission curves of X-ray broad beams through common shielding materials, for the contrast-enhanced digital mammography (CEDM) imaging technique, using Monte Carlo simulations. Simulations were performed for anode/filter combinations of W/Rh and W/Ag, for tube potentials between 25 and 35 kVp, employed for low energy (LE) imaging, and for W/Cu, W/Ti and Mo/Cu between 35 and 49 kVp, for high energy (HE) imaging. Fitting parameters for each transmission curve were also obtained. Methods: Transmission curves were simulated using the Monte Carlo code PENELOPE. The geometric model adopted was composed by the breast compression paddle and the following common shielding materials: lead, steel, plate glass, concrete, gypsum, and wood. The obtained curves were fitted to the Archer equation, in order to determine their fitting parameters α, β, and γ. Results: Transmission curves for LE and HE spectra showed different behaviors. On average, values of half-value layer at high attenuation for LE spectra, at 35 kVp, are 2.36 times greater than those at 25 kVp, while for HE spectra, at 49 kVp, excepting for wood, are 2.39 times greater than those at 35 kVp. Results for fitting parameters showed that α values decrease with tube potential, whereas the behavior of β and γ values depends on the spectrum and shielding material. Conclusions: The results obtained and the fitting parameters provided can be useful for evaluating the shielding design of this technique, since there are significant differences between results for the LE and HE spectra, evidentiating the importance of considering appropriate transmission data. © 2021, Sociedade Brasileira de Engenharia Biomedica.