Real-time estimation system for mean glandular dose in mammography

The purpose of this study was to construct a system that calculates mean glandular dose (MGD) in mammography in real-time on the radiology information system (RIS) network. Measurement of the half-value layer (HVL) and exposure dose were measured according to the Japanese mammographic quality control manual. A parallel plate chamber (10X5-6M; soft X-rays only) was used for measurement. Exposure dose was measured from 26 to 32 kV. Effective energy (Eeff [keV]) could be determined from tube voltage (V [kV]) using the measure of the HVL according to the following equations: for the Mo/Mo combination, Eeff=0.1325V+11.80; for the Mo/Rh combination, Eeff=0.1435V+12.20; for the Rh/Rh combination, Eeff=0.1724V+11.29. Exposure output (XmAs [mR/mAs]), which can be determined from dosimetry per 1 mAs, becomes the following equation if effective energy is expressed as a variable: for the Mo/Mo combination, XmAs=2.1329 Eeff2-57.784 Eeff+392.71; for the Mo/Rh combination, XmAs=1.1919 Eeff2-31.924 Eeff+212.23; and for the Rh/Rh combination, XmAs=2.6929 Eeff2-82.831 Eeff+643.54. The MGD conversion factor (DgN [mGy/mR]) can be determined from effective energy using the American College of Radiology (ACR) protocol according to the following equation: for the Mo/Mo combination, DgN=(0.3962 Eeff-4.3178)·10-3; for the Mo/Rh combination, DgN=(0.3495 Eeff-3.5479)·10-3; and for the Rh/Rh combination, DgN=(0.4498 Eeff-5.0448)·10-3. However, in these cases, compression breast thickness (CBT) was 4.2 cm, and the ratio of adipose and glandular tissue was 50/50. MGD can be determined using mAs obtained from mammography, exposure output (XmAs), MGD conversion factor (DgN), and source-skin distance compensation factor (SSDcf) according to the following equation: MGD [mGy]=mAs·XmAs [mR/mAs]·DgN [mGy/mR]· SSDcf where SSDcf={64/(64-CBT [cm]){2. (author)