1. Characterisation of microcalcification clusters
on 2D digital mammography (FFDM) and
digital breast tomosynthesis (DBT): does DBT
underestimate microcalcification clusters?
Results of a multicentre study.
4. Digital breast tomosynthesis (DBT) is a novel mammography
technique capable of studying the breast using 3D
reconstructions of the tissue from multiple low-dose digital
mammographic images, acquired along a 15 to 50 degree
arc.
This process increases lesion visibility because of the
reduction of overlapping breast tissue.
Recently, digital breast tomosynthesis alone or combined with
digital mammography has been shown to detect cancers
occult to 2D mammography.
5. Its potential role as a screening test has also been
recently demonstrated in large scale prospective
screening trials.
In addition, a recent meta-analysis showed that DBT may
have a higher sensitivity and specificity in breast
diagnosis than digital mammography.
Regarding radiation dose, an increase in radiation dose
due to the 3D acquisition has been detected with an
increase of entrance skin air kerma and average
glandular dose.
6. Very few reports in the literature have compared FFDM and
DBT for classification of microcalcification clusters.
Some authors have outlined that DBT may underestimate BI-
RADS cluster classification compared to FFDM.
In theory, using DBT, the radiologist may be more accurate in
characterising some breast lesions to reduce the rate of false
positive breast biopsies but it is unknown whether this applies
to microcalcifications.
The purpose of this study was to assess differences between
DBT and FFDM in the characterisation of microcalcification
clusters using the standard BI-RADS classification.
8. Institutional Review Board approval and written informed
consent were received.
The study was undertaken in three different centres: IRCCS
San Martino Hospital-University of Genoa, IRCCS Molinette
Hospital Torino and Bolzano Central Hospital.
10. A total of 120 mammographic examinations showing
microcalcification clusters (MCs) were identified based on
searching the electronic databases of the radiological reports
between January 2010 and June 2012.
All women had digital mammography using a Selenia
Dimensions unit with integrated 2D and 3D mammography
done in the COMBO mode (acquisition of 2D plus 3D images
in the same session).
The X-ray tube moves over a 15° arc.
The 2D and 3D images are acquired at the same examination
with a single breast position and compression.
Each 2D and 3D image consisted of a bilateral two-view
(mediolateral oblique and craniocaudal) mammogram.
11. Only MCs with both DBT and FFDM images available and with
a follow-up of at least 12 months were included in this study.
Clearly benign calcified lesions such as calcified
fibroadenomas were not included in the analysis.
Final histology was used to confirm malignant cases.
Bilateral mediolateral oblique and craniocaudal views were
considered an image set for FFDM, whereas the 3D
mediolateral oblique and craniocaudal view reconstructed
images and the video clip were considered the DBT image set.
12. Six breast radiologists, each with at least 7 years of
experience in digital mammography and 2 years of
experience in the clinical use of DBT, read the FFDM and
DBT image sets prospectively and assigned a BI-RADS
score to each cluster.
The two image sets (FFDM and DBT) were read
independently in sessions separated by at least 4 weeks to
minimise recall bias.
13. Data analysis
The overall sensitivity and specificity with a 95 %
confidence interval were calculated for FFDM and DBT
using final histology and clinical follow-up as the reference
standard.
Comparative sensitivity of FFDM and DBT was calculated
classifying results as positive or negative as follows:
benign (R1-R2) vs. malignant (R3-R4-R5).
15. The calcification clusters with complete data comprised 107
of 120, with 13 clusters excluded because of incomplete
follow-up (n=10 patients lost to follow-up) or to missing
DBT data in the hospital PACS (n=3).
All clusters were visible on both DBT and FFDM.
The mean age was 51.7 years.
The benign/malignant ratio of MC was 66/41.
16. There were 11/107 discordant results where DBT classified
calcification clusters as R2, whereas FFDM classified these
as R3 in 9 and R4 in 2.
Three of these (3/107=2.8 %) were malignant and incorrectly
underclassified as R2 on DBT.
Eight (8/107=7.5 %) were non malignant and were correctly
classified as R2 on DBT but were incorrectly classified as R3
on FFDM.
17.
18. Left craniocaudal (CC) view in FFDM and DBT shows a microcalcification
cluster that was classified with the BI-RADS classification as R4 in FFDM
and R2 in DBT (ductal carcinoma at histology)
19. DBT correctly classified 8/107 discordant clusters that
were benign.
The patients with these clusters may have avoided
unnecessary biopsies based on DBT.
On large numbers these data may be relevant since they
imply that DBT could potentially reduce the burden of
recall for benign calcifications and overtreatment in a
screening setting.
22. This study focused on evaluation of MC because clinical
experience with DBT for the assessment of breast lesions has
revealed some potential pitfalls with the imaging of
microcalcifications.
Possible underlying reasons for this include that the
morphology of some calcifications in DBT appear to be
different when compared to the 2D FFDM images or that
some calcifications seem less visible on DBT.
This study stated that FFDM appears to be slightly more
sensitive than DBT for the detection of calcification.
However, diagnostic performance using BI-RADS was not
significantly different between the two modalities.
23. The global analysis of the data suggests that DBT has the
potential disadvantage of missing a very small proportion of
malignant MCs.
Therefore, if only 3D is used, there is a risk of lesion
underestimation if the only mammographic sign is a
microcalcification cluster, so it is possible that a small
proportion of lesions such as DCISs could be missed using
only 3D.
At present, trial evidence supports use of 2D plus 3D
images (and not only 3D images) for the purpose of
screening.
25. Conclusion
This study suggests that microcalcification clusters may be
classified differently on FFDM and DBT using the BI-RADS
classification, although this only occurred in a minority of
cases.
In discordant cases, DBT-assigned lower BI-RADS classes
compared to FFDM, and DBT may have missed some
malignant and premalignant lesions.
On the other hand, DBT may have the advantage of avoiding
unnecessary biopsies in patients with benign conditions
manifest as microcalcifications.
26. Conclusion
Most MCs are similarly scored on BI-RADS on FFDM and
DBT, but DBT has the potential disadvantage of
underclassifying a very small proportion of malignant
lesions that manifest as MC.
Authors suggest careful evaluation and further research
on the use of DBT for assessment of microcalcifications.
27. Take home message
2D plus 3D images (and not only 3D images)
should be used for the purpose of screening
to avoid underestimation of MC clusters if 3D
images are used alone.
