Breast tomosynthesis and digital mammography: a comparison of diagnostic accuracy

Objective

Our aim was to compare the ability of radiologists to detect breast cancers using one-view breast tomosynthesis (BT) and two-view digital mammography (DM) in an enriched population of diseased patients and benign and/or healthy patients.

Methods

All participants gave informed consent. The BT and DM examinations were performed with about the same average glandular dose to the breast. The study population comprised patients with subtle signs of malignancy seen on DM and/or ultrasonography. Ground truth was established by pathology, needle biopsy and/or by 1-year follow-up by mammography, which retrospectively resulted in 89 diseased breasts (1 breast per patient) with 95 malignant lesions and 96 healthy or benign breasts. Two experienced radiologists, who were not participants in the study, determined the locations of the malignant lesions. Five radiologists, experienced in mammography, interpreted the cases independently in a free-response study. The data were analysed by the receiver operating characteristic (ROC) and jackknife alternative free-response ROC (JAFROC) methods, regarding both readers and cases as random effects.

Results

The diagnostic accuracy of BT was significantly better than that of DM (JAFROC: p=0.0031, ROC: p=0.0415). The average sensitivity of BT was higher than that of DM (∼90% vs ∼79%; 95% confidence interval of difference: 0.036, 0.108) while the average false-positive fraction was not significantly different (95% confidence interval of difference: −0.117, 0.010).

Conclusion

The diagnostic accuracy of BT was superior to DM in an enriched population.About 1 in 8–10 females develop breast cancer during their lifetime [1,2]. Screening mammography plays a key role in the detection of breast cancer at an early stage. Based on incidence of interval cancers it has been suggested that a radiologist reading screen-film mammograms might miss 16–30% of cancers detectable on the mammograms [3]. Mammography cancer detection varies widely: estimates of sensitivity have been reported from 68% (or as low as 48% for extremely dense breasts) to 88%, with specificities ranging from 82% to 98%. These results suggest that there is considerable room for improvement in mammography [4,5]. Digital mammography (DM) was expected to improve the performance of breast cancer detection compared with screen-film mammography (SFM). In most clinical trials the overall sensitivity has been higher for DM, but, since the specificities have also been lower, only a few studies have been statistically significant in favour of DM [5]. In a subset of females under 50 years of age in the Digital Mammographic Imaging Screening Trial study, there was a significantly improved diagnostic accuracy in DM compared with SFM [5].Because a mammogram is a two-dimensional (2D) projection of the breast onto the detector plane, overprojected healthy tissue (anatomical noise) can hamper breast cancer detectability. Anatomical noise is known to have a greater impact than quantum noise on the detection of certain breast cancers (e.g. masses) [6,7]. Two views—mediolateral oblique (MLO) and craniocaudal (CC)—can partially compensate for the overlapping anatomical noise, but this depends on the radiologist''s ability to mentally fuse the two images.Breast tomosynthesis (BT) collects 2D projection views over a limited angular range, which allows reconstruction of thin slices of the breast volume. Reduced anatomical noise from superimposed tissues is expected to improve breast cancer detection compared with DM. In CT where hundreds of projection images are acquired covering 360°, the anatomical noise can be reduced to a larger degree, but it is difficult to image the entire breast volume using CT, particularly close to the chest wall. Moreover, the average glandular dose is higher with CT, as is imaging time and the cost of the device. While there is ongoing research that may solve these issues [8-10], BT has a number of potential advantages and there are currently commercialised units.Previous studies of observer performance of BT compared with DM have shown contradictory results, varying from a statistically significant advantage for BT [11-13] to no clear advantage for BT [14-18]. Non-blinded pilot studies have been performed at our institution that suggest improved sensitivity of BT over DM [19,20].The aim of the current study was to compare the diagnostic accuracy of one-view BT with conventional two-view DM using an enriched population.