Real-time estimation system for mean glandular dose in mammography.
OBJECTIVE
The purpose of this study was to construct a system that calculates mean glandular dose (MGD) in mammography in real-time on the RIS network.


METHODS
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.


RESULTS
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 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) x 10(-3); and for the Rh/Rh combination, DgN = (0.4498 Eeff - 5.0448) x 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.


CONCLUSIONS
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 x XmAs [mR/mAs] x DgN [mGy/mR] x SSDcf where SSDcf = (64/(64 - CBT [cm]))2.
Matsumoto
Mitsuhiro
M
Department of Medical Physics, Osaka University Graduate School of Medicine, Suita, Japan.
Inoue
Shinichi
S
Honda
Ikuko
I
Yamamoto
Shuji
S
Ueguchi
Takashi
T
Ogata
Yuji
Y
Johkoh
Takeshi
T
D001940:Breast / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006801:Humans; D008327:Mammography; D008962:Models, Theoretical; D011786:Quality Control; D011829:Radiation Dosage