Inter-observer variability in mammography screening and effect of type and number of readers on screening outcome

Abstract

We prospectively determined the variability in radiologists' interpretation of screening mammograms and assessed the influence of type and number of readers on screening outcome. Twenty-one screening mammography radiographers and eight screening radiologists participated. A total of 106,093 screening mammograms were double-read by two radiographers and, in turn, by two radiologists. Initially, radiologists were blinded to the referral opinion of the radiographers. A woman was referred if she was considered positive at radiologist double-reading with consensus interpretation or referred after radiologist review of positive cases at radiographer double-reading. During 2-year follow-up, clinical data, breast imaging reports, biopsy results and breast surgery reports were collected of all women with a positive screening result from any reader. Single radiologist reading (I) resulted in a mean cancer detection rate of 4.64 per 1000 screens (95% confidence intervals (CI)=4.23-5.05) with individual variations from 3.44 (95% CI=2.30-4.58) to 5.04 (95% CI=3.81-6.27), and a sensitivity of 63.9% (95% CI=60.5-67.3), ranging from 51.5% (95% CI=39.6-63.3) to 75.0% (95% CI=65.3-84.7). Sensitivity at non-blinded, radiologist double-reading (II), radiologist double-reading followed by radiologist review of positive cases at radiographer double-reading (III), triple reading by one radiologist and two radiographers with referral of all positive readings (IV) and quadruple reading by two radiologists and two radiographers with referral of all positive readings (V) were as follows: 68.6% (95% CI=65.3-71.9) (II); 73.2% (95% CI=70.1-76.4) (III); 75.2% (95% CI=72.1-78.2) (IV), and 76.9% (95% CI=73.9-79.9) (V). We conclude that screener performance significantly varied at single-reading. Double-reading increased sensitivity by a relative 7.3%. When there is a shortage of screening radiologists, triple reading by one radiologist and two radiographers may replace radiologist double-reading.

Figure 1

Radiologist single-reading vs radiologist double-reading: mammography-screening outcome at 2-year follow-up. At radiologist double-reading, a woman was referred for additional work-up if the mammogram was considered to be positive by both radiologists or, in the case of discrepant readings, if at least one radiologist considered referral necessary after consensus meeting. SDC=screen-detected cancer.

Figure 2

Radiologist single-reading combined with radiographer double-reading: mammography-screening outcome at 2-year follow-up. A woman was referred for additional work-up if the mammogram was considered to be positive at radiologist single-reading and/or at radiographer double-reading. SDC=screen-detected cancer.

Figure 3

Radiologist double-reading followed by radiologist review of positive cases at radiographer double-reading: mammography-screening outcome at 2-year follow-up. SDC=screen-detected cancer; SDC_next=cancer detected at subsequent screening; IC=interval cancer.