Stability of volumetric tissue composition measured in serial screening mammograms

The purpose of this study is to investigate the categorization and variation of serial mammogram pairs in dense and non-dense classes. When introducing density based stratified screening, the differences in density between screening rounds should be as small as possible to prevent women and clinicians losing confidence in the stratification scheme. A total of 8843 mammogram pairs (current and prior, mean screening interval 22.65 months) were categorized in dense and non-dense cases based on percent density and volume of glandular tissue. The reproducibility of the categories (prior to current) was tested with simple kappa statistics and the causes for a category change were investigated. When comparing two examinations, the majority of pairs remained in the same category, with κ= 0.783 and κ = 0.696 based on percent density and glandular tissue volume respectively. For most women, glandular tissue volume and percent density decreases with age. However in 3.2% (4.6%) of the pairs an examination was classified as non-dense followed by dense based on percent density (glandular tissue volume). Natural circumstances can lead to a change in category, for example glandular tissue volume decreases with age, or increases with the use of HRT. However a higher reproducibility in categorization in dense and not-dense classes based on automatic breast density calculations was found, than reported in the literature based on visual assessment. The reproducibility was higher when using percent density for classification.