DBT-supplemented screening resulted in significant increases in screen-detected cancers and specificity. However, no significant change was observed in the rate, size, node status, or grade of interval cancers. ClinicalTrials.gov: NCT01248546.

ammography screening reduces breast cancer mortality through early detection of small node-negative cancers (1,2). Digital mammography (DM) has two inherent limitations: low sensitivity in dense breasts because of a "masking effect" caused by overlying parenchyma and low specificity because summation of normal parenchyma can simulate a lesion. Results from retrospective studies (3-5) and prospective trials (6-8) have confirmed the potential of digital breast tomosynthesis (DBT) to address these limitations. Several studies implementing DBT in screening used "combo mode" DM + DBT (3-7). However, use of this mode results in a doubling of radiation dose. Synthetic mammography (SM) images are a potential solution to this challenge and require no additional radiation dose. The purpose of our prospective Oslo Tomosynthesis Screening Trial (OTST) was to compare diagnostic accuracy for independent reading of DM to DM + DBT, addition of computer-aided detection (CAD) to DM, and use of SM instead of DM in combination with DBT for breast cancer screening. Materials and Methods Hologic (Marlborough, Mass) sponsored this study by providing equipment and financial support for additional radiologist readings. Authors had full control of all data. The trial was approved by the regional ethical committee (clinical trial number NCT01248546). Written informed consent was required from all participants.

he sensitivity of digital mammography (DM) is lower in women with dense breasts than in those with lower breast density (1). Breast density is also associated with higher false-positive rates and recall rates (2) due to superposition of normal glandular tissue that can mimic cancer. The woman's age has an impact on mammography screening as breast density decreases (3) and cancer incidence increases. The distribution of cancers shifts toward less-aggressive slower-growing cancers with increasing age (4). It has been shown that mammography screening has a lower sensitivity (1) and higher false-positive rate (2) among younger women. Digital breast tomosynthesis (DBT) generates pseudo three-dimensional (3D) images where a single section of anatomy is in focus. The rest is blurred, with greater magnitude proportional to the distance from the focus plane. The screening performance of DBT for specific density and age groups may be different from that of DM, as DBT potentially can reduce masking and resolve superposition of breast tissue. Prospective (5-11) and retrospective (12-18) studies have shown that the integration of DBT improves the cancer detection or recall rates for both fatty and dense breasts and in age groups relevant for mammography screening. Data are limited in almost entirely fatty and extremely dense breasts. Two large studies compared DBT and DM in women with extremely dense breasts, with one study finding an increased cancer detection rate with DBT (5) and the other finding similar rates for DBT and DM (13). Therefore, there is a need for more data from large prospective trials.

The optimal volumetric threshold of 10% using automatic assessment would classify breast parenchyma as fatty or dense with substantial accuracy and consistency compared to radiologists' BI-RADS categorization, which suffers from high inter-observer variation.

The main purpose was to compare average glandular dose (AGD) for same-compression digital mammography (DM) and digital breast tomosynthesis (DBT) acquisitions in a population based screening program, with and without breast density stratification, as determined by automatically calculated breast density (Quantra). Secondary, to compare AGD estimates based on measured breast density, air kerma and half value layer (HVL) to DICOM metadata based estimates. AGD was estimated for 3819 women participating in the screening trial. All received craniocaudal and mediolateral oblique views of each breasts with paired DM and DBT acquisitions. Exposure parameters were extracted from DICOM metadata. Air kerma and HVL were measured for all beam qualities used to acquire the mammograms. Volumetric breast density was estimated using Quantra. AGD was estimated using the Dance model. AGD reported directly from the DICOM metadata was also assessed. Mean AGD was 1.74 and 2.10 mGy for DM and DBT, respectively. Mean DBT/DM AGD ratio was 1.24. For fatty breasts: mean AGD was 1.74 and 2.27 mGy for DM and DBT, respectively. For dense breasts: mean AGD was 1.73 and 1.79 mGy, for DM and DBT, respectively. For breasts of similar thickness, dense breasts had higher AGD for DM and similar AGD for DBT. The DBT/DM dose ratio was substantially lower for dense compared to fatty breasts (1.08 versus 1.33). The average c-factor was 1.16. Using previously published polynomials to estimate glandularity from thickness underestimated the c-factor by 5.9% on average. Mean AGD error between estimates based on measurements (air kerma and HVL) versus DICOM header data was 3.8%, but for one mammography unit as high as 7.9%. Mean error of using the AGD value reported in the DICOM header was 10.7 and 13.3%, respectively. Thus, measurement of breast density, radiation dose and beam quality can substantially affect AGD estimates.

Based on international references and medical physicists' practical experiences, a comprehensive QA protocol for CT systems is proposed, including both acceptance and constancy tests. The protocol may serve as a reference for medical physicists in the Nordic countries.

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