A randomized controlled trial of digital breast tomosynthesis versus digital mammography in population-based screening in Bergen: interim analysis of performance indicators from the To-Be trial

Abstract

Objectives: To describe a randomized controlled trial (RCT) of digital breast tomosynthesis including synthesized two-dimensional mammograms (DBT) versus digital mammography (DM) in a population-based screening program for breast cancer and to compare selected secondary screening outcomes for the two techniques.

Methods: This RCT, performed in Bergen as part of BreastScreen Norway, was approved by the Regional Committees for Medical Health Research Ethics. All screening attendees in Bergen were invited to participate, of which 89% (14,274/15,976) concented during the first year, and were randomized to DBT (n = 7155) or DM (n = 7119). Secondary screening outcomes were stratified by mammographic density and compared using two-sample t-tests, chi-square tests, ANOVA, negative binomial regression and tests of proportions (z tests).

Results: Mean reading time was 1 min 11 s for DBT and 41 s for DM (p < 0.01). Mean time spent at consensus was 3 min 12 s for DBT and 2 min 12 s for DM (p < 0.01), while the rate of cases discussed at consensus was 6.4% and 7.4%, respectively for DBT and DM (p = 0.03). The recall rate was 3.0% for DBT and 3.6% for DM (p = 0.03). For women with non-dense breasts, recall rate was 2.2% for DBT versus 3.4% for DM (p = 0.04). The rate did not differ for women with dense breasts (3.6% for both). Mean glandular dose per examination was 2.96 mGy for DBT and 2.95 mGy for DM (p = 0.433).

Conclusions: Interim analysis of a screening RCT showed that DBT took longer to read than DM, but had significantly lower recall rate than DM. We found no differences in radiation dose between the two techniques.

Key points: • In this RCT, DBT was associated with longer interpretation time than DM • Recall rates were lower for DBT than for DM • Mean glandular radiation dose did not differ between DBT and DM.

Keywords: Breast cancer; Digital breast tomosynthesis; Mammography; Mass screening; Randomized controlled trial.

Conflict of interest statement

Guarantor

The scientific guarantor of this publication is Solveig Hofvind.

Conflict of interest

The authors of this manuscript declare no relationships with any companies whose products or services may be related to the subject matter of the article.

Statistics and biometry

No complex statistical methods were necessary for this paper.

Informed consent

Written informed consent was obtained from all subjects (patients) in this study.

Ethical approval

Institutional review board approval was obtained.

Methodology

• prospective

• randomized controlled trial

• performed at one institution

Figures

Fig. 1

Study design of the To-Be trial in Bergen, a randomized controlled trial using digital breast tomosynthesis in combination with synthesized 2D images (DBT) versus digital mammography (DM), in Breast Screen Norway. Excluded because of a lack of data on mammographic density

Fig. 2

Study design and study population for interim analyses after 1 year of running the To-Be trial in Bergen, 2016

Fig. 3

Mean glandular dose (MGD) per examination among women screened during the first year of the To-Be trial, overall and by Volpara density grade (VDG), stratified by imaging technique (digital breast tomosynthesis including synthesized 2D mammograms [DBT] or digital mammography [DM])

Fig. 4

Rates of consensus and recalls by cumulative number of DM (dotted line) and DBT (solid line) screen-readings during the first year of the To-Be trial in Bergen, 2016