Indices for the evaluation of glandular dose heterogeneity in full-field digital mammography

摘要

This study aims to evaluate the indices of glandular dose heterogeneity in full-field digital mammography. The distributions of GD in a breast phantom with a skin layer of 4 mm were determined using the Monte Carlo method with simulated x-ray fluence spectra. First, the GD to air kerma (GD/K-air) volume histogram was obtained from the GD distributions, which were indicated by the glandular volume (%) as a function of GD/K-air. The GD indices, namely, the maximum glandular dose (GD(2%)) and glandular volume percentage (%) receiving at least the mean glandular dose (MGD) (V-MGD) were calculated from the GD/K-air volume histogram. Next, the scatter plots of GD(2%)/MGD and V-MGD were drawn as functions of the normalised mean glandular dose (DgN). Finally, (GD(2%))(i) and (V-MGD)(i) were obtained from the relationship between the GD indices and DgN for 596 clinical irradiation cases based on individual irradiation conditions. The values of GD(2%)/MGD were more affected by breast thickness than glandularity and tube voltage, and they decreased according to the power law of DgN for all the target/filter combinations. The values of V-MGD were proportional to DgN and decreased with increase in the compressed breast thickness. The values of (MGD)(i) and (GD(2%))(i) for 596 clinical irradiation cases were estimated to range from 0.6-3.0 mGy to 1.1-7.0 mGy, respectively, and (V-MGD)(i) was in the range 32%-48%. (GD(2%))(i) and (V-MGD)(i) are mainly affected by breast thickness. These indices are useful for the evaluation of glandular dose heterogeneity in mammography.