Volume 12 Issue 8 - August 2014
                       
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Breast Tomosynthesis
     
  In the three years since the introduction of breast tomosynthesis into clinical practice, several large clinical trials have compared screening with conventional digital mammography to screening with both tomosynthesis and conventional digital mammography

  These studies provide strong evidence that the combination of tomosynthesis and digital mammography is clinically superior to digital mammography alone in that:
The recall rate is lower
The cancer detection rate, especially for invasive cancers, is higher
  By reducing recall rates, breast tomosynthesis may reduce patient anxiety and lower the costs of further testing


Tomosynthesis Procedure
Scheduling
Further Information
References

Breast tomosynthesis is an X-ray imaging method in which an X-ray tube moves in an arc, acquiring a series of views that are post-processed to create images showing thin (typically 1 mm) slices of breast tissue. By minimizing the obscuring presence of overlying structures seen in digital mammography, tomosynthesis can reveal the characteristic margins of a tumor more clearly (Figure 1). In addition, it yields fewer suspicious images that can result from superimposition of normal or benign structures (Figure 2). Breast tomosynthesis, which was invented and developed by Daniel B. Kopans, MD, and Richard H. Moore at the MGH, was approved by the U.S. Food and Drug Administration (FDA) in early 2011 as a screening method for detecting breast cancer, based on a clinical study that demonstrated the superiority of tomosynthesis plus digital mammography in detecting cancer while reducing the number of false positive readings compared to digital mammography alone.

Figure 1. Mediolateral oblique (MLO) images of the right breast from a screening tomosynthesis plus digital mammography examination. (A) The mammogram demonstrates no suspicious calcifications, mass, or architectural distortion. (B) A single tomosynthesis slice demonstrates a spiculated mass in the superior right breast, which was confirmed on additional imaging (not shown). Subsequent ultrasound-guided core biopsy confirmed a 7 mm grade 1 invasive ductal carcinoma.
Figure 1. Mediolateral oblique (MLO) images of the right breast from a screening tomosynthesis plus digital mammography examination. (A) The mammogram demonstrates no suspicious calcifications, mass, or architectural distortion. (B) A single tomosynthesis slice demonstrates a spiculated mass in the superior right breast (white arrow), which was confirmed on additional imaging (not shown). Subsequent ultrasound-guided core biopsy confirmed a 7 mm grade 1 invasive ductal carcinoma.


Figure 2. MLO images of the left breast of another patient from a screening tomosynthesis plus digital mammography examination. (A) The mammogram demonstrates an asymmetry in the left superior breast. (B) A single tomosynthesis slice demonstrates that the asymmetry is due to a normal vascular structure. As a result, the patient did not need to be recalled for additional imaging.
Figure 2. MLO images of the left breast of another patient from a screening tomosynthesis plus digital mammography examination. (A) The mammogram demonstrates an asymmetry in the left superior breast (white arrow). (B) A single tomosynthesis slice demonstrates that the asymmetry is due to a normal vascular structure (white arrow). As a result, the patient did not need to be recalled for additional imaging.


In the three years since the approval of tomosynthesis, five large studies conducted in both community and academic settings have confirmed the advantages of tomosynthesis plus digital mammography over digital mammography alone (Table 1). Three of these studies demonstrated a statistically significant drop in recall rates from a range of 8.7–12.0% for digital mammography to 5.5–9.1% when tomosynthesis is added. In the largest of these studies, which combined data from 13 academic and non-academic breast centers, 11 out of 13 found that their recall rates dropped during the period after they introduced tomosynthesis. The two centers that did not experience a reduction in recall rates were characterized as having a short period of implementation or a small volume of cases per radiologist, suggesting that radiologists’ performance may improve with experience. The reduction in recall rates appeared to be greater in younger women and women with dense breasts.

Four of the five studies also showed a higher rate of cancer detection with tomosynthesis plus digital mammography (range, 5.3–8 per 1,000 cases) compared to digital mammography alone (range, 4.04–6.4 per 1,000 cases), although not all results were statistically significant (Table 1). The most recent study, by Friedewald et al., is the most compelling for several reasons. It compared performance in a screening setting in the U.S before and after the implementation of tomosynthesis, rather readings of digital mammography and tomosynthesis that were acquired at the same time.  It also included a large enough cohort to achieve statistical significance not only in terms of reduced recall rate and increased positive predictive values for recall and biopsy, but also showed an increase in cancer detection rate. Moreover, virtually all of the increase in cancer detection could be attributed to invasive forms of cancer; tomosynthesis more than doubled the rate of lobular cancer detection, while the study showed no change in the number of cases of ductal carcinoma in situ (DCIS).

Table 1. Comparisons of Tomosynthesis and Digital Mammography versus Digital Mammography Alone
Recall (R) or False Positive (FP) Rate Breast Cancer Detection Rate per 1,000 Cases
Tomosynthesis & Digital Mammography Digital Mammography P-value Tomosynthesis & Digital Mammography Digital Mammography P-value
Haas et al.,
2013
R = 8.4%
(n=6,100)
R = 12.0% (n=7,058) <.01 5.7 5.2 .70
Skaane et al.,
2013
FP = 5.3%
(n=12,621)
FP = 6.1% (n=12,621) <.001 8 6.1 .001
Ciatto et al.,
2013
FP = 3.5%
(n=7,292)
FP = 4.4% (n=7292) <.0001 8.1 5.3 .0001
Rose et al.,
2013
R = 5.5%
(n=9,499)
R = 8.7% (n=13,856) <.001 5.37 4.04 .18
Friedwald et al.,
2014
R = 9.1%
(n=173,663)
R = 10.7% (n=281,187) <.001 5.4 4.2 <.001

The ultimate test for the effectiveness of tomosynthesis will be a demonstration of a decrease in cancer mortality, which will not be possible to know until sufficient time has elapsed to measure changes. However, several large clinical trials have demonstrated that mammography decreases the death rate by up to 30%. As tomosynthesis plus digital mammography detects more invasive cancers than mammography, it could potentially decrease mortality to a greater degree than mammography alone. Regardless of it effects on mortality rate, tomosynthesis provides patient benefits by reducing recall rates and increasing the positive predictive value of recall by 49%. These findings show that tomosynthesis reduces the "harm" related to patient anxiety and has the potential to decrease the cost of breast cancer screening because it is associated with fewer follow-up diagnostic examinations.

Tomosynthesis Procedure
The procedure for breast tomosynthesis is similar to digital mammography. Both require careful positioning and compression of the breast to acquire craniocaudal and mediolateral oblique views. The procedure for tomosynthesis differs in that the breast is imaged in a series of exposures as the X-ray tube moves through a limited arc. Current protocols require that tomosynthesis be combined with digital mammography to allow easy comparison of side-to-side symmetry. The total time for the combined examination is approximately 10 seconds.

By performing both tomosynthesis and digital mammography, the radiation exposure is approximately double that of digital mammography alone, although the total exposure is well within the American College of Radiology guidelines for radiation dose for mammography. The FDA has approved technology to create a synthesized mammogram from tomosynthesis data but it is not yet validated in clinical practice.

The reporting system for tomosynthesis is the same as the BI-RADS system used for digital mammography (Table 2). In cases of suspicious findings, diagnostic imaging procedures may include additional mammographic studies, ultrasound, or MRI. MRI may also be used as a screening method for women who have significant risk factors (e.g., first-degree relative diagnosed with breast cancer, BRCA1 or BRCA2 gene mutation). In addition, MRI is sometimes used to stage newly diagnosed cancer and guide treatment planning.

BIRADS score Interpretation Recommended Actions
0 Incomplete Return for additional imaging
1 Normal Routine screening in 12 months
2 No change/benign Routine screening in 12 months
3 Probably benign Follow up imaging in 6-12 months
4 Suspicious Surgical consultation, biopsy
5 Highly suspicious Surgical consultation, biopsy
6 Known cancer

Scheduling
The American Cancer Society, the National Comprehensive Cancer network, the American Congress of Obstetricians and Gynecologists, the American College of Radiology, and other organizations recommend annual mammograms for women 40 and older. Breast tomosynthesis is the standard of care for all patients who are screening for breast cancer at Mass General with the exception of the associated facilities on Martha’s Vineyard and Nantucket. Appointments can be made through ROE (inside Partners network) or ROE Portal (outside Partners network) or by calling 617-724-XRAY (9729).

Further Information
For further information on breast tomosynthesis, visit www.massgeneral.org/3dmammo or contact G. Scott Gazelle, MD, MPH, PhD, Deborah ter Meulen, MD, or Elizabeth A. Rafferty, MD, Breast Imaging Division, Department of Radiology, Massachusetts General Hospital, at 617-726-3093.

We would like to thank Deborah ter Meulen, MD, G. Scott Gazelle, MD, MPH, PhD, Bethany L. Niell, MD, PhD, and Elizabeth A. Rafferty, MD, Breast Imaging Division, Department of Radiology, Massachusetts General Hospital, for their assistance and advice on this issue.


References

Kopans, DB. (2014) Digital breast tomosynthesis from concept to clinical care. AJR 202:299-308

Ciatto S, et al. (2013). Integration of 3D digital mammography with tomosynthesis for population breast-cancer screening (STORM): a prospective comparison study. Lancet Oncol 14:583-9

Friedewald SM, et al. (2014). Breast cancer screening using tomosynthesis in combination with digital mammography. Jama 311:2499-507

Haas BM, et al. (2013). Comparison of tomosynthesis plus digital mammography and digital mammography alone for breast cancer screening. Radiology 269:694-700

Rose SL, et al. (2013). Implementation of breast tomosynthesis in a routine screening practice: an observational study. AJR Am J Roentgenol 200:1401-8

Skaane P, et al. (2013). Comparison of digital mammography alone and digital mammography plus tomosynthesis in a population-based screening program. Radiology 267:47-56



©2014 MGH Department of Radiology

Janet Cochrane Miller, D. Phil., Author
Raul N. Uppot, Editor


 

 

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