Monte Carlo Evaluation of Normalized Glandular Dose Coefficients in Mammography

The mean glandular dose in mammography is evaluated via the normalized glandular dose coefficients (DgN), calculated via Monte Carlo simulations. The conversion from dose to the homogenous mixture to dose in the glandular tissue is made by considering an energy-dependent correction factor, G, which is the weighted mean of the energy absorption coefficients of adipose and glandular tissues. The authors implemented a GEANT4 code and evaluated, in the range 8-80 keV, the influence on the calculation of DgN values by (1) the method of G-weighting the dose, (2) the inclusion of bremsstrahlung radiation and (3) the energy threshold under which electrons are not tracked. The results for monochromatic DgN show that evaluating G retrospectively causes an underestimation up to 5 %, and that not considering bremsstrahlung or setting high electron energy cutoff may cause a bias up to 1 %, in the calculation of monochromatic DgN. These deviations may be negligible for polychromatic mammographic spectra.