The determination of patient dose in full field digtal mammography

Abstract

Full field digital mammography (FFDM) is the new technology of digital imaging for clinical use. It is an application where an emphasis on patient dose management and risk reduction are required. Nevertheless, the breast tissue has a relatively high sensitivity to some adverse effects of radiation and significant risk of radiation induced carcinogenesis associated with the radiation absorbed dose to the breast. The objective of this study is to determine the average glandular dose (AGD) for Thai female undergoing FFDM system and to identify the factors affecting it. This study involves 749 women underwent mammography examinations using the FFDM system, Hologic Lorad Model Selenia during the period from February 2006 to February 2007. The system was installed at the Department of Radiology, King Chulalongkorn Memorial Hospital. The quality control of FFDM system is routinely performed. AGD displayed on the monitor is verified by dosimetry and calculation methods. The information has been extracted from the digital mammographic image in DICOM header. The AGD, entrance skin exposure (ESE) and technique factors were displayed on the monitor of FFDM system. The factors affecting AGD per woman were studied using a multivariable analysis. Mean (+-SD) value for patient age was 51.3 (+-8.6) years and mean compressed breast thickness (CBT) for craniocaudal (CC) and mediolateral oblique (MLO) views were 6.2 cm and 6.1 cm, respectively. The mean ESE per image was 11.89 mGy for CC and 11.84 mGy for MLO views. The mean AGD per image (with grid) was 1.80 mGy for CC and 1.81 mGy for MLO views. The mean AGD per woman was 3.62 mGy therefore, a new dose reference level (DRL) of 2.0 mGy (third quartile) per image is proposed. The mAs is directly affected AGD by stepwise regression (p-value < 0.001). The result could not represent the FFDM examination in Thailand because it is a localized survey at one department. In addition, the quality control of the system and the calibration of the flat panel detectors play an important role in the patient dose achieved. The mean AGD per image obtained for both CC and MLO views was 91.2% lower than the reference level of 3.0 mGy as recommended by the American College of Radiology (ACR).