Radiation dose in breast CT imaging with monochromatic x-rays: Simulation study of the influence of energy, composition and thickness

Recent developments have shown that high resolution phase contrast x-ray computed tomography (CT) of the breast can be performed at clinically compatible doses. Results have yet been obtained in vitro on full breasts, and the clinical translation of the technique seems more and more possible. This work presents a method to quickly estimate the average dose in the organ using the software GATE. The influence of different parameters on the dose distribution, like breast composition and thickness, and for preclinical test, the presence of a skin/PMMA external layer, has been investigated. Several correction factors, to be applied to the given dose database, are also introduced to allow the use of these results in geometries different from those studied here. An energy optimization study is presented that considers also the influence on the energy choice of x-ray detector. A simple analytical method to estimate the best energy that minimizes the dose-transmittance ratio in CT imaging is presented and compared with the results of simulations.