Laurie Lee Fajardo MD, MBA, Presenter: Scientific Advisory Board, Hologic, Inc Scientific Advisory Board, Koninklijke Philips NV

Limin Yang MD, PhD, Abstract Co-Author: Nothing to Disclose

Mark Bennett Williams PhD, Abstract Co-Author: Institutional research agreement, Hologic, Inc.

To characterize the dosimetric properties of clinical digital breast tomosynthesis (DBT) systems during a single combo (2D + 3D) scan in a screening environment.

Mean glandular radiation dose as recorded in the DICOM header was extracted for 950 asymptomatic patients (mean age 56.3 yrs; range 28 – 90 yrs) undergoing routine 2D + 3D combo breast screening (CC &/or MLO compressions, 3449 breasts) on one of two Hologic Dimensions systems. Dose was evaluated as a function of compressed breast thickness (CBT). Analysis was performed for individual BIRADS tissue density categories as determined by expert radiologists.

BIRADS breast tissue density among the study group was: almost entirely fatty (11.1%); scattered fibroglandular densities (51.5%); heterogeneously dense (28.2%) and extremely dense (9.2%). CBT ranged from 1.4 - 10.7 cm (mean = 6.0 cm). For 2D images with CBT < 7 cm (n = 2610), a tungsten/rhodium anode/filter combination was used with dose ranging from 0.54 - 4.49 mGy (mean = 1.62 mGy). For 2D images with CBT > 7 cm (n = 839), tungsten/silver anode/filter combination was used and dose ranged from 1.43 - 4.88 mGy (mean= 2.46 mGy). For DBT images, a tungsten/aluminum anode/filter was used for all compressed thicknesses (n = 3449) with dose ranging from 0.94 - 4.69 mGy (mean = 2.39 mGy). The total dose for a 2D+3D combo exam ranged from 1.56 mGy - 8.88 mGy (mean = 4.12 mGy), with 28 of 3504 (0.8%) combo exposures ≥ 3 mGy for breasts with CBT ≤ 4.2 cm. The relative dose contribution from the 2D and 3D portions of the scan changed monotonically with changing BIRADS classification, with 3D+2D dose ratio increasing from ~1 for extremely dense breasts to > 1.5 for fatty breasts.

Based on current automatic exposure control algorithms used in DBT, reconstructing 2D images from DBT projection images will reduce radiation dose by ~50% for dense breasts and ~40% for fatty breasts, enabling opportunities to refine the dosimetric properties of DBT and improve image quality.

Breast screening using 2D + 3D combo DBT has demonstrated improved breast cancer detection and reduced FP (recall) rates. Dose in the majority of combo exposures is ≥3mGy; thus, substituting “synthetic 2D” for conventional DM images affords opportunities to better refine the dosimetric properties and image quality of DBT.

Fajardo, L, Yang, L, Williams, M, Dosimetric Properties of a Clinical DBT System: Relative Dose Contributions of 2D vs. 3D Exposures for Varying Breast Density.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14004210.html