Average Glandular Dose and Entrance Surface Dose in Mammography

In general, dose evaluation for mammography uses average glandular dose (AGD). In mammography, entrance surface dose (ESD) is high, which is well known, but actual clinical data of ESD are not reported so much. This study investigated AGD and ESD for patients whose doses were estimated from 200 mammography examinations using European Organization for Quality-Assured Breast Screening and Diagnostic Services (EUREF) protocol. In addition, ESD is compared to breast surface dose for multidetector CT. The digital mammography system (Amulet, Fujifilm Solutions) has full-field flat panel detector. This system uses an automatic exposure control system, which adjusts to exposure output in order to obtain appropriate image density in clinical practice. First of all, AGD and ESD for PMMA accrediting phantom were estimated, using automatic exposure control system, every 10 mm from 10 to 60 mm. Then, patient-based AGD and ESD were estimated from 200 women (the age of 40 to 70) who had a mammography in Toyota memorial hospital. Finally, breast surface dose in an anthropomorphic phantom was measured using thermoluminescent dosimeters during chest CT scan. On examination of 40mm PMMA, the AGD and the ESD were 1.61 mGy and 6.06 mGy, respectively. The ESD was 3.8 times higher compared with the AGD. The result of calculating patient data shows that AGD and ESD per view averaged 1.71 mGy and 6.60 mGy. The breast surface dose for CT was measured 15.07 mGy. This dose was 1.1 times slightly higher compared with two-view mammography. A mammography examination involves twice of exposure to obtain craniocaudal and mediolateral oblique views. The result of study indicates that a total ESD of a mammographic examination is equally high to breast surface dose of CT, the dose for mammography should be evaluated both AGD and ESD.