Last Updated : May 13, 2015
Traditional two-dimensional (2D) mammography captures two static images of the breast. One particular shortcoming of 2D technology is the overlapping of breast images that can decrease accuracy of interpretation. With digital breast tomosynthesis (DBT), an X-ray beam sweeps in an arc of 15 to 50 degrees (depending on the manufacturer) across the breast, and an electronic detector digitally captures between nine and 25 X-ray projection images.1-6 These images are generally captured in two views: craniocaudal (head-to-toe direction) and mediolateral oblique (angled side-view).2,3,5 The data from these projections are used in computer algorithms to reconstruct a series of parallel thin "slices" (tomographic images) corresponding to 0.5 mm to 1 mm intervals through the breast. The slices create a three-dimensional (3D) volume of data that represents the breast's tissue structures.
The objective of DBT is to improve detection of breast cancer compared with 2D mammography screening by:
Mammography systems are designated as Class III medical devices by Health Canada. In Canada and the United States (US), DBT screening must include both 2D and 3D image sets (2D plus 3D)10,11 (Health Canada, Ottawa, Ontario: personal communication, 28 Feb 2015); however, this is not the case in Europe.2
In 2009, Health Canada licensed the Selenia Dimensions 2D/3D Mammography System (device licence #79158, Hologic Inc., Danbury, Connecticut),7 which is marketed in Canada by Christie Innomed.8,9 Selenia Dimensions received US Food and Drug Administration (FDA) approval in February 2011 for routine clinical use in screening or diagnostic work-up.
The SenoClaire Breast Tomosynthesis System by GE Medical Systems (Buc, France) was licensed for use in Canada in May 2014 (device licence #93289)7 and in the US in August 2014.13
In April 2015, Siemens Healthcare (Erlangen, Germany) received US FDA approval for its True 3D Breast Tomosynthesis option for the MAMMOMAT Inspiration digital mammography system.12
Selenia Dimensions and SenoClaire received CE (Conformité Européene) clearance in the European Union (EU) in 200814 and 2013,15 respectively.
Other manufacturers are seeking regulatory approval for DBT systems, including the Giotto Tomo system (IMS, Bologna, Italy) (currently approved in the EU)16 and the AMULET Innovality (Fujifilm Europe, Düsseldorf, Germany).17
Breast cancer is the most common cancer among Canadian women (excluding non-melanoma skin cancers) and the second leading cause of cancer death in this group. Canadian estimates for 2014 predicted that 24,400 women would be diagnosed with breast cancer (26% of all new cancer cases in women) and 5,000 would die from the disease (14% of all cancer deaths in women).18 Challenges with breast cancer are not only its incidence rate but also the lack of proven preventive strategies — early detection and treatment are currently the main approaches.19
Screening mammography is often credited with significantly reducing the number of deaths from breast cancer.20 The Canadian Breast Cancer Foundation states that over the past three decades, mammography has helped to reduce deaths from breast cancer by more than 35%.21 However, a lack of consensus remains about the benefits of breast screening as well as its potential harms, shortcomings, and indications.2,22-24
The Canadian Task Force on Preventive Health Care recommends that women aged 50 to 74 at average risk of breast cancer have mammography screening every two to three years, with mammography not generally recommended for those aged 40 to 49.25 In contrast, the US Preventive Services Task Force recommends that average-risk women aged 50 to 74 be screened every two years and that screening decisions for women under age 50 be individualized based on context and patient values.26
The main screening tool for breast cancer is 2D screening mammography, but its 75% to 80% sensitivity is not ideal.4,27 This means that, of 100 women who truly have breast cancer, only 75 to 80 will have their cancers detected through a screening mammogram. Sensitivity decreases to 50% for women with dense breasts27 because their lesions may be hidden, and some breast cancers may be missed as a result.4,28 False-positive test results lead to recalls for 12% to 16% of women undergoing their first screens and 4% to 6% of women undergoing subsequent screens.29 These women are subjected to further radiation exposure and biopsies.6 Recent attention has focused on a number of mammography issues, including the rate of false-positives (in part due to the fact that normal breast tissue, when overlapping, can appear abnormal with 2D technology); issues related to false-positive recalls; and the fact that many biopsies after screening are unnecessary, as they turn out to be negative for cancer.28,30,31
There are several options for follow-up after screening mammography. The most common are diagnostic mammograms and ultrasound. An ultrasound can differentiate cysts from solid masses and may increase the accuracy of cancer detection by 50% compared with mammography alone, particularly in high-risk women and those with dense breasts.6 However, ultrasounds also result in false-negative and false-positive findings, with benign diagnoses in 70% to 90% of cases.6 Magnetic resonance imaging (MRI) has higher sensitivity than 2D mammography, but it has a number of limitations. For example, the positive predictive value and specificity are low, tumour diameter can be overestimated, the cost is high, and some patients cannot undergo MRI, such as those with metallic implants or claustrophobia.6,27
The Canadian Association of Radiologists (CAR) published guidance on breast imaging and intervention in late 2013,32 including a description of DBT and its applications and limitations.
At that time, DBT was in the active stages of testing and early stages of clinical use, and the CAR guidance noted that it was unclear what the role of DBT would be in general population screening, subgroup screening, and diagnosis.
A peer-reviewed literature search was conducted using the following bibliographic databases: MEDLINE, PubMed, Embase, and the Cochrane Library (2015, Issue 1). Grey literature was identified by searching relevant sections of the CADTH Grey Matters checklist (http://www.cadth.ca/resources/grey-matters). No methodological filters were applied. The search was limited to English language documents published between January 1, 2012 and January 21, 2015. Regular alerts were established to update the search until April 1, 2015. Conference abstracts were excluded from the search results.
A number of studies of DBT for breast screening were identified. The seven largest studies (each enrolling more than 10,000 women)28,31,33-38 were selected for detailed review in this report (Table 1). All studies were based on established breast screening programs using Hologic Selenia Dimensions technology for 3D screening, with six studies conducted in the US28,31,33-35,38 and the seventh in Norway.36 The Norwegian study was prospective (women received both types of imaging and served as their own controls), while the American studies were retrospective (four were before-and-after studies of outcomes once the new technology was installed33-35,38 and two enrolled groups of women who received the older and newer technologies at different sites over the same time period).28,31 The Norwegian study involved double reading with arbitration: all images in the study were interpreted by two independent radiologists who had to reach a consensus for the need for recall before a woman was asked to return for more imaging.36 Study sizes ranged from approximately 13,000 to approximately 450,000 women. Of the six studies that reported sources of research support and conflicts of interest, three noted ties to Hologic.35,36,38 Additional study details are presented in Appendix A.
The seven studies collectively examined recall rates and cancer detection outcomes for more than 600,000 women, primarily in the US. Each of the six American studies showed a statistically significant reduction in the rates of women recalled for further investigations, ranging from 15% to 37%, but the Norwegian study did not — possibly because its methodology, which included arbitration through double reading of test results, led to a higher chance that a test result would be flagged for recall.
Differences between 2D and 2D plus 3D screening in cancer detection rates were statistically significant in only three of the seven studies: the prospective Norwegian study36 and two American before-and-after retrospective reviews.28,35 The other four studies found no significant difference in rates of cancer detection per 1,000 women screened,31,33,34,38 although one of the US studies38 found a trend toward lower invasive cancer detection rates of 2.8 versus 4.3 per 1,000 women for 2D versus 2D plus 3D, respectively (P = 0.07.) In addition, of the three studies that looked at biopsy rates after screening (Appendix A),33,35,38 only one found a statistically significant result — 18.1 versus 19.3 per 1,000 women for 2D versus 2D plus 3D, respectively (P = 0.004).35 Two studies assessed the positive predictive value of biopsy, and neither found a significant result.28,34
Radiation dose is an important concern, due to the radiosensitivity of breast tissue. Dose of radiation varies depending on number of views, exposure controls, and other factors.6,39 With DBT, each exposure is only a fraction of a 2D dose, but many images are captured and the overall dose generated by combined 2D plus 3D units can be twice that of 2D alone.1,4,5,39-42 However, this higher dose is still below the limit accepted by the US Mammography Quality Standards Act for a single screening mammography exam.38,43 A recent innovation is to replace the 2D step in combined imaging with "synthetic" 2D views reconstructed from the DBT acquisitions. This can potentially eliminate the requirement for 2D imaging altogether and halve the overall radiation dose compared with that of 2D alone.1,4,9,40,41 Another concern with 2D mammography is the pain of breast compression, which can affect screening compliance; patient discomfort may be reduced with DBT as there is less need to maximize breast compression to eliminate tissue overlap.6,10
Table 1: Summary of Included Studies
|First Author (Year), Study Design||N||Outcomes|
|Recall Rate After Screening (2D vs. 2D+3D)||Cancer Detection Rate per 1,000 Screened(2D vs. 2D+3D)|
Before-and-after retrospective review
|454,850||10.7% vs. 9.1% (P < 0.001);
|4.2 vs. 5.4 (P < 0.001)|
|59,617||16.2% vs. 13.6% (P < 0.0001);
|4.9 vs. 6.3 (P = 0.035)|
|13,158||12.0% vs. 8.4% (P < 0.01);
|5.2 vs. 5.7 (P = 0.70)|
Before-and-after retrospective review
|25,498||9.3% vs. 6.4% (P < 0.00001);
|5.4 vs. 4.6 (P = 0.44)|
Before-and-after retrospective review
|26,299||10.4% vs. 8.8% (P < 0.001);
|4.6 vs. 5.5 (P = 0.32)|
Before-and-after retrospective review
|23,355||8.7% vs. 5.5% (P < 0.001)
|4.0 vs. 5.4 (P = 0.18)|
|12,621||2.9% vs. 3.7% (P = 0.005); 27% increase for 2D+3D (but double reading with arbitration was used)||7.1 vs. 9.4 (P < 0.001)|
2D = two-dimensional; 2D+3D = two-dimensional plus three-dimensional (combined); 3D = three-dimensional; N = number of patients; vs. = versus.
The technology cost of newer digital mammographic units is high, with DBT capability costing about US$750,000.20,40 In the US, DBT is still considered investigational and there is no fee item to facilitate billing by providers. This is also the case in Canada; for example, the British Columbia, Alberta, and Ontario physicians' fee guides do not include DBT.44-46 According to the literature, including some of the studies cited here, the current paradigm in the US is for the provider to either absorb the increased cost or charge patients an extra US$50 on top of the fee for 2D mammography for this imaging step.5,20,28,43,47 One US report describes a range of additional charges for DBT from US$25 to US$250.48
A US cost-effectiveness analysis43 of biennial screening of women aged 50 to 74 with dense breasts calculated an incremental cost per life-year gained of US$70,500 for 2D plus 3D screening versus 2D alone. Clinical data were obtained from the Norwegian trial36 and the base case cost of additional DBT was set at US$50 (US data were not available at the time of the analysis). The calculated incremental cost per quality-adjusted life-year (QALY) was about US$54,000 (neither cost per cancer detected nor impact on mortality rates were reported). Assuming that DBT led to moderate improvements in sensitivity and specificity, 405 false-positive results were avoided per 1,000 women after 12 screening rounds and 0.5 breast cancer-related deaths per 1,000 women were averted. The cost-effectiveness was most sensitive to the additional cost of tomosynthesis; increasing the cost of adjunct tomosynthesis did not affect the relative cost-effectiveness of combined screening until the added cost of tomosynthesis exceeded US$87, for a total screening cost of US$226.43
A number of breast imaging technologies are under development, including breast MRI, contrast-enhanced mammography, ultrasound with elastography or microbubbles, and dual-energy mammography (spectral mammography). Other breast imaging technologies being explored include breast computed tomography (CT) scanning (a dedicated CT system that provides 3D images without compression), 3D ultrasound, radionuclide breast imaging, and positron emission tomography (PET).27,39,49
In Canada, a 2014 article reported the installation of three Selenia Dimensions DBT units at Toronto's Princess Margaret Cancer Centre, with plans for further expansion.8 News items report that other breast tomosynthesis units have been installed at a British Columbia centre and at the Women's Breast Health Centre in Ottawa.50,51
A 2012 survey of 1,800 physician members of the US Society of Breast Imaging explored the extent of DBT diffusion.48 The survey response rate was 30%, and results showed that 30% of respondents reported using DBT. At the extremes, 51% of respondents had a single DBT unit, whereas for 6% of respondents, all units were DBT. About 80% of respondents used DBT for screening, although only 20% of these offered it to all screening patients. The use of DBT was twice as common in academic practices as it was in private practices.
Experts have identified a number of implementation issues:
Cite as: Foerster, V. Tomosynthesis (3D Mammography) for Breast Cancer Screening [Issues in emerging health technologies, Issue 135]. Ottawa: Canadian Agency for Drugs and Technologies in Health; 2015.
Issues in Emerging Health Technologies is a series of concise bulletins describing drug and non-drug technologies that are not yet used (or widely diffused) in Canada. The contents are based on information from early experience with the technology; however, further evidence may become available in the future. These summaries are not intended to replace professional medical advice. They are compiled as an information service for those involved in planning and providing health care in Canada.
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BREAST CANCER SCREENING — 2D ALONE VERSUS 2D PLUS 3D MAMMOGRAPHY
|Author (Year); Country; Study Years and Type||Population||Intervention (All 2D and 3D)||Comparator||Outcomes|
|Friedewald et al. (2014);35 US; before-and-after retrospective review of 2D cohort (2010-2011) vs. 2D+3D cohort (2011-2012) at 13 centres||N = 454,850: 62% had 2D and 38% had 3D as well as 2D||Hologic Selenia Dimensions||2D DM (devices NR)||
|Greenberg et al. (2014);28 US; retrospective review of 2 cohorts screened over the same time span (2011-2012) at different sites (2D or 2D+3D)||N = 59,617 (mean age 60 years): 65% chose 2D and 35% chose 3D (most paid an extra fee of US$50)||Hologic Selenia Dimensions||2D DM mammogram (Hologic Selenia)||
|Haas et al. (2013);31 US; 2011-2012; retrospective review of 2 cohorts screened over the same time span at different sites (2D or 2D+3D)||N = 13,158: 54% had 2D and 46% had 3D as well as 2D||Hologic Selenia Dimensions||2D DM (Hologic Selenia)||
|Lourenco et al. (2015); 34 US; before-and-after retrospective review of 2D cohort (2011-2012) vs. 2D+3D cohort (2012-2013)||N = 25,498 (mean age 55 years; range 25 to 90): 49% had 2D and 51% had 3D||Hologic Selenia Dimensions||2D DR mammogram (Senographe, GE Medical)||
|McCarthy et al. (2014);33 US; before-and-after retrospective review of 2D cohort (2010-2011) vs. 2D+3D cohort (2011-2013)||N = 26,299: 41% had 2D and 59% had 3D as well as 2D||Hologic Selenia Dimensions||2D DM (devices NR)||
|Rose et al. (2013);38 US; before-and-after retrospective review of 2D cohort (2010) vs. 2D+3D cohort (2011-2012)||N = 23,355: 59% had 2D and 41% had 3D as well as 2D||Hologic Selenia Dimensions||2D DM (Hologic Selenia)||
|Skaane et al. (2013);36 Norway; prospective study with women serving as their own controls (4 exams done using one compression), 2011-2012, DOUBLE READING with arbitration||N = 12,621 women aged 50 to 69||Hologic Selenia Dimensions Unit (2D/3D + synthesized 2D/3D)||Hologic Selenia Dimensions Unit (2D + 2D with CAD)||
2D = two-dimensional; 2D+3D = two-dimensional plus three-dimensional (combined); 3D = three-dimensional; CAD = computer-aided detection; CI = confidence interval; DBT = digital breast tomosynthesis; DM = digital mammography; NR = not reported; NSD = not significantly different; OR = odds ratio; PPV = positive predictive value; vs. = versus.