SF 15b - Breast cancer screening with tomosynthesis: the time is now
1. To learn about the need for improving breast cancer screening.
2. To learn about alternative screening techniques.
3. To learn about the potential benefits of DBT as compared with other modalities.
A main limitation of conventional mammography (FFDM) is the poor sensitivity in women with dense breast parenchyma. During the last decade there has been much discussion how to improve the quality of breast cancer screening, especially for women at increased risk. Focusing on personalized (individualized) screening, ultrasound and MRI has been considered the most important adjuncts to mammography. It is important to distinguish between low-volume (“individualized”) and high-volume (“population-based”) screening regarding implementation of new techniques. An emerging mammographic technique that might significantly improve screening is digital breast tomosynthesis (DBT). Cancer visibility and conspicuity is increased using tomosynthesis, and DBT has significantly higher sensitivity (cancer detection rate) than FFDM. DBT has also a higher specificity (lower recall rates). Furthermore, DBT can replace conventional cone-mag views for evaluation of non-calcified indeterminate lesions, which also is an important contribution for reducing recalls in screening programs. Implementation of DBT with synthetic 2D reconstructed from the 3D data has several advantages compared with other modalities: Ultrasound is time-consuming and has a low specificity; MRI is expensive and availability is limited. Other modalities are still at a research level. DBT might easily be incorporated into existing programs, and transition from FFDM to DBT would be less challenging than the transition from screen-film to FFDM a decade ago. DBT might be the next improvement of population-based breast cancer screening. Cost-effectiveness studies and studies on outcomes including number and stage of interval cancers and subsequent round cancers are still to be desired.
1. To learn about recalls and cancer detection in the USA DBT screening studies.
2. To understand the false positive and the false negative interpretations in screening with tomosynthesis.
3. To understand the influence of breast density and age on the performance of DBT screening.
Mammography is the best screening test for the early detection of breast cancer. Mammography had not changed for many years until the advent of digital imaging technology. Digital technology allowed the development of digital breast tomosynthesis (DBT), an advanced application, informally called 3D mammography (in contrast to conventional 2D DM). DBT has arrived on the world stage in time to address many of the limitations of mammography. Dense tissue has always been the challenge of mammography due to the masking effect. Trials have shown that cancer detection rate with DBT is improved as the cancers are “unmasked” as the issue of overlapping tissue or summation artefacts are eliminated. Additionally, recent criticism of mammography has centred false-positive examinations and overdiagnosis. In numerous trials, the call back rates are lower when DBT is used compared to standard DM. Fewer women are asked to return for summation shadows as DBT easily resolves these at interpretation. A recent multicentre study published in the Journal of the American Medical Association (JAMA) found that when tomosynthesis is used in addition to digital screening mammography, there is a 41% increase in invasive cancer detected, 15% decrease in unnecessary callbacks for false alarms and a 29% increase in the detection of all breast cancers. The conclusion is that DBT finds more of the invasive, harmful cancers and saves women the anxiety and cost of having additional screenings for what turns out to be a false alarm.
Screening with digital breast tomosynthesis in Europe: tumour characteristics and potential harms including overdiagnosis
1. To learn about the tumour characteristics of cancers detected with tomosynthesis.
2. To understand the potential influence of DBT screening on interval cancer rate and next round cancers.
3. To learn about the potential harms of tomosynthesis screening with special focus on so-called "overdiagnosis".
The introduction of a new more expensive technique to breast screening requires careful analysis of the cost-benefit. DBT has been shown to increase the sensitivity and specificity of the detection of breast cancer especially in younger women, those with increased breast density (BIRADS C & D) and for those readers who are less experienced. However, it should not be assumed there will be a mortality benefit. One method is to use surrogate end points - tumour size and stage. However, information on tumour aggressiveness determines whether the additional cancers might have caused harm. There is increased sensitivity in cancers presenting as spiculate masses and also asymmetric density or distortion both of which tend to be associated with less aggressive cancers. In the prospective studies, there were relatively few additional DCIS cases being found and slightly more grade 1 cancers compared to grade 2 & 3 cancers. The three large prospective trials cannot report interval cancer rates as each case was read by all combinations but one small American series has reported a non-significant decrease in the number of interval cancers. Tumour size should decrease in incident rounds following the introduction of DBT. The potential harms of DBT are increased number of biopsies for benign lesions or even further excision. The radiation dose is small but can be avoided using synthetic 2D with DBT. The unknown harm is the increase in “overdiagnosis” (diagnosis of cancers that would not otherwise have been found in the woman’s lifetime).
1. To discuss radiation dose, number of DBT projections, and the need for conventional or synthetic 2D images in combination with DBT.
2. To learn about hanging protocols, reading time, and potential solutions for reducing the interpretation time.
3. To understand the "IT issues" in DBT screening implementation.
Clinical benefits of digital breast tomosynthesis (DBT) in screening application have been demonstrated. However, there is concern about some technical aspects which should be analysed before implementing tomosynthesis in screening. The first concern regards radiation dose, which is supposed to be minimized when x-ray techniques are used to image healthy population. Dose differences depending on the tomosynthesis and the number of projections will be discussed, along with dose dependence from the clinical protocol (number of views, tomosynthesis alone or in combination with standard mammography), and the role of synthetic mammograms in this respect. The second negative aspect associated to the introduction of tomosynthesis is the increase of the interpretation time; learning curve is crucial, but also software developments like navigation tools or computer-aided detection (CAD) systems might help the reduction of the reading time. Appropriate hanging protocols should be defined to allow comparison with prior DBT examinations in subsequent screening rounds. Finally, the large amount of data produced by DBT versus standard mammography have a significant IT impact. IT infrastructure should be adapted to handle datasets that can be from 10 to 20 times the size of standard digital mammography images. The storage space needs to be increased, but also pre-fetching mechanism could be necessary to cope with the time necessary to retrieve DBT datasets from the PACS. Advantages of the implementation of the DICOM standard format for DBT images will be shortly discussed.