Research in Medicine

Background: Average Glandular Dose (AGD), entrance skin Air Kerma (ESAK), and Normalized Glandular Dose (DgN) are the main dosimetric quantities in mammography. Breast tissue composition is one of the factors affecting DgN values. In the present study, both homogeneous and heterogeneous breast tissues are assumed evaluating their impacts on DgN values.
Methods: Homogeneous breast phantom with different glandular fractions simulated and DgN values were calculated for the homogeneous phantom. Also, a heterogeneous breast phantom was simulated, considering that adipose tissue is in the background and glandular tissue is in the form of spheres which are in the breast phantom. By changing the radius of glandular tissue, the glandular fraction in heterogeneous breast phantom was changed. DgN values were also calculated for the heterogeneous breast phantom. DgN values in both homogeneous and heterogeneous breast phantoms were evaluated and the results were compared.

Results: DgN values depend on glandular fraction in both homogeneous and heterogeneous breast phantoms. As the glandular fraction increased, DgN values reduced almost linearly. Breast tissue heterogeneity affected DgN values, too; this effect is related to the distribution of the glandular tissue in the heterogeneous breast phantom, so that considering the change in the distribution of glandular tissue in the heterogeneous breast phantom, the relative difference in DgN value between homogeneous and heterogeneous phantom was variable between -47 to +77 percent.
Conclusion: In the previous studies in which DgN coefficients were calculated, and this coefficient was used in mammography dosimetry, the effect of heterogeneity of breast tissue was not considered. According to the results of the present study and the evident effect of heterogeneity 3 of glandular and fat tissue on the breast phantom, a correction factor to the DgN values is suggested.