A mammographic phantom image reconstruction through Monte Carlo techniques

Mammographic phantoms are employed during quality control test in breast screening locations and other health centres. These quality controls are performed to achieve the image quality required to detect breast abnormalities, ensuring the minimum risk to radiographied women. The aim of this study is the development of a methodology to reproduce the image of a mammogram during a routine exposure in a breast screening programme. In a first step, the CIRS 11A (MAMMO PHANTOM SP01) mammographic phantom has been simplified and modelled with the Monte Carlo transport code MCNP-4c2. Different tallies (F2 and F5) have been used to score the photon flux under the phantom, and a group of aluminium layers (99.9% purity) have been employed to reconstruct the characteristic curve, which transforms output air kerma in a grey-scale level. The code has been modified to produce photons in a semi-cone, allowing any polar and azimuthal angle. Furthermore, different tally bins have been introduced to count photons in each pixel of the final image, improving computer time simulations. The horizontal resolution target has been reproduced at different tube loadings and pixel pitches. The reconstructed images agree with the range of values, indicating that this method would be suitable for training purposes, phantom designing or dose calculations