Quality of the screening procedure: Miller claimed that all equipment was new and that a quality assurance was in place [11, 6]. The responsible physicist stated [30], “quality was far below state of the art – even at that time (early 1980s). Problems … from inadequate equipment, … inappropriate imaging technique and lack of….specialized training….”. This was confirmed by several others including external reviewers [28, 29, 34], who specified that “training for mammography technologists or radiologists and a quality assurance were not present”. The study had initially been overseen by two highly renowned advisors (S. Feig and W. A. Logan). They resigned from the study after 3 years due to unacceptable quality. Subsequent external review rated image quality as acceptable in < 40 % of the cases during 1980-1984, in 1985 in about 60 %, and in 1986-7 in < 85 %. Problems included incomplete inclusion of the breast tissue, unsharp images, low image contrast, over- or underexposed images [28, 38] (Fig. 3). Overall, a very large number of interval cancers (143/575) resulted in this annual screening trial. It exceeds the rate, which in modern quality-assured mammography screening is considered acceptable for year one of the interval, by a factor of about 3. According to the reviewers, the above problems of poor image quality, inadequate training of personnel and readers may have accounted for the majority of the excess interval cancers. A subgroup analysis by Moskowitz [39] reported an increase of the detection rate with improving image quality at the end of the study, supporting a correlation with image quality.
Fig. 3 Images demonstrating the significant changes of technology between 1984, 1987 (CNBSS-study), and a follow-up mammogram of the same patient of 1993. Even though the later technology is still far from present contrast resolution, it becomes obvious that on the former mammograms almost no structures can be discerned in 80 % of the breast making detection of both masses and microcalcifications almost impossible. Images reproduced courtesy of Dr. Roberta Jong, Sunnybrook Health Sciences Centre, Toronto Canada