Radiation doses from digital breast tomosynthesis system

Abstract

Background : Breast tomosynthesis is a new technology to improve the sensitivity and specificity of mammography by eliminating tissue overlap. Breast tomosynthesis is essentially a modification of a digital mammography (2D) to enable the acquisition of a three-dimensional (3D) volume of thin section data. Images are reconstructed in conventional orientations by using reconstruction algorithms similar to those used in computed tomography (CT).

Objective : To determine the average glandular dose (AGD) and the entrance surface air kerma (ESAK) from cranio-caudal (CC) and medio-lateral oblique (MLO) projections in 2 dimension and 3 dimension imaging modes.

Design : Retrospective descriptive data

Setting : Breast Imaging Unit, Department of Radiology, King Chulalongkorn Memorial Hospital

Methods : Patients’ data from digital breast tomosynthesis (DBT) system were analyzed in terms of the compressed breast thickness (CBT, mm), peak kilovoltage (kVp), tube current time (mAs), average glandular dose (AGD, mGy) and the entrance surface air kerma (ESAK, mGy) in 2D and 3D image sets from one compression.

Results : One hundred and ninety eight female breast cancer patients with breastconserving surgery were studied using digital breast tomosynthesis system from January-December 2012. The CBT, kVp and mAs were recorded when the tungsten target with rhodium or silver filters were chosen in 2D and the tungsten target with aluminum filter were chosen in 3D images. The mean compressed breast thickness (CBT) was 54.5 mm for craniocaudal, CC and 55.0 mm for medio-lateral oblique, MLO views. The mean AGD and ESAK for 4 views of both sides in 2D and 3D were 1.7, 6.5 and 2.0, 7.0 mGy respectively. The mean AGD and ESAK in 3D imaging mode were 16.1 % and 6.1 % higher than the mean AGD and ESAK in 2D imaging mode. No significant relationship was found between AGD and CBT in 2D imaging mode of a correlation coefficient of 0.36 and a good correlation coefficient of 0.87 in 3D imaging mode.

Conclusion : The mean CBT was 54.7 mm, the mean AGD from digital breast tomosynthesis (DBT) system was 2.0 mGy, the mean AGD of full field digital mammography (FFDM) CC views 1.65 mGy and MLO was 1.75 results in overall mean AGD of 1.7 mGy. Both values of 2D and 3D are still lower than 3.0 mGy limit for single view of dose reference level (DRL) set by MQSA.