6th International Workshop on Breast Densitometry and Breast ...

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6 th <strong>International</strong> <strong>Workshop</strong> on Breast Densitometry
and Breast Cancer Risk Assessment
VISUAL ANALOGUE SCALE ASSESSMENT OF PERCENTAGE BREAST DENSITY: A
STUDY OF AGREEMENT BETWEEN OBSERVERS AND WITH INTERACTIVE
THRESHOLDING
Jamie C. Sergeant 1 , Mary Wilson 2 , Nicky Barr 2 , Ursula Beetles 2 , Caroline Boggis 2 , Sara Bundred 2 , Megan
Bydder 2 , Soujanya Gadde 2 , Emma Hurley 2 , Anil Jain 2 , Yit Lim 2 , Liz Lord 2 , Valerie Reece 2 , D. Gareth
Evans 2 , Anthony Howell 2 , Susan M. Astley 1
1 Centre for Imaging Sciences, Institute for Population Health, University of Manchester, Manchester, UK:
2 Nightingale Centre and Genesis Prevention Centre, University Hospital of South Manchester,
Manchester, UK
Aim: The measurement of percentage breast density on a visual analogue scale (VAS) has been shown to
have an association with breast cancer risk comparable to that of interactive thresholding software such as
Cumulus (Sunnybrook Health Sciences Centre, Toronto, Canada). While interactive thresholding is too
labour intensive to implement in a breast screening programme for the purposes of prospective risk
estimation, the quick and simple VAS method is more well-suited to this application. However, for VAS
density measurement to be satisfactorily used for this purpose, there must be comparability between
estimates produced by different observers. We examine the agreement between a group of observers
assessing VAS breast density and their agreement with Cumulus.
Method: 120 screening cases were sampled from the Predicting Risk Of Cancer At Screening
(PROCAS) study, a large clinical study based in Manchester, UK, which aims to predict the risk of breast
cancer when women attend routine breast screening. The cases all had Full-Field Digital Mammography
(FFDM) images acquired on GE Senographe Essential equipment. The breast density of the cases was
independently assessed by 12 experienced mammographic readers using a separate VAS for each
radiographic projection (craniocaudal and mediolateral oblique) of both breasts. In addition, a trained and
validated Cumulus user also estimated the density for each image. Assessment of inter-observer
agreement and agreement with Cumulus was performed using the Bland-Altman limits of agreement
approach and the concordance correlation coefficient (CCC). All density estimates were also discretised
to the four BI-RADS breast composition categories and agreement on this ordinal scale measured with
Cohen’s weighted kappa.
Results: The maximum observed difference between estimates by two readers assessing the same case
was 67.75 percentage points, while the mean difference between pairs of readers ranged from 0.76 to
28.58 percentage points and the mean difference from Cumulus ranged from 0.38 to 22.98 percentage
points. 95% limits of agreement between reader pairs, between which 95% of differences are expected to
lie, were (-6.96, 18.62) at their narrowest and (-59.13, 1.97) at their widest, while between readers and
Cumulus they ranged from (-32.55, -3.29) to (-49.71, 3.94). Pairwise CCC values ranged from 0.44 to
0.92, while the overall CCC across the 12 readers was 0.70. Concordance with Cumulus ranged from 0.48
to 0.87. Pairwise kappa values for the BI-RADS classification ranged from 0.37 to 0.84 for the 12 readers,
with a mean of 0.66. Kappa values between the readers and Cumulus ranged from 0.40 to 0.80.
ABSTRACTS
Conclusion: A lack of agreement was found between the readers visually assessing breast density and a
comparable lack of agreement was also found between the readers and Cumulus. This group of readers
had varying levels of experience of VAS breast density assessment, but were all routinely performing
estimation in the PROCAS study. The current study suggests that for VAS density to be used for risk
stratification and personalised screening, inter-observer variation must be accounted for, either through
standardised training or by applying a correction to results after reading has been performed.
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