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DOI: 10.1148/radiol.2432060253
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Breast Cancer Detection Rate: Designing Imaging Trials to Demonstrate Improvements1

Yulei Jiang, PhD, Diana L. Miglioretti, PhD, Charles E. Metz, PhD, and Robert A. Schmidt, MD

1 From the Department of Radiology, University of Chicago, 5841 S Maryland Ave, MC2026, Chicago, IL 60637 (Y.J., C.E.M., R.A.S.); and Group Health Cooperative, Seattle, Wash (D.L.M.). Received February 9, 2006; revision requested April 7; revision received June 7; accepted July 7; final version accepted September 20. Supported in part by the National Cancer Institute through grants R01 CA92361 and U01CA86076. Address correspondence to Y.J. (e-mail: y-jiang{at}uchicago.edu).


Figure 1
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  		Figure 1: Histogram of single-reader cancer detection rates for 510 radiologists who read at least 500 screening mammograms during the study. The mean cancer detection rate is 3.91 cancers (standard deviation, 1.93) per 1000 screening mammograms.

 

Figure 2
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  		Figure 2: Probabilities as a function of the number of readers in a trial for observing no additional cancers detected (left), one-half or more additional cancers detected per 1000 screening mammograms (middle), and a statistically significant increase in cancer detection rate (ie, statistical power) (right), given a postulated increase of one additional cancer detected per 1000 screening mammograms. Correlation of individual readers' cancer detection rates between the two arms of a trial is not included. Variability in the observed single-reader cancer detection rates caused the discrepancies between the postulated and observed changes in cancer detection rates. Curves are grouped by single-reader total screening mammogram volume; parenthetical numbers indicate the number of readers for each volume category. See text and Figure 3 for confidence intervals. Sample sizes refer to one arm of a two-arm trial.

 

Figure 3
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  		Figure 3: Modification of the probabilities shown in Figure 2 due to the effect of correlation in the observed single-reader cancer detection rates between two arms of a trial. The correlation was measured from two separate studies of screening mammography (see Statistical Analyses section). The Pearson correlation coefficient was 0.44. Shaded areas represent 95% confidence intervals. The confidence band with the effect of correlation taken into account (not shown) was 2%–4% wider than the corresponding confidence band without correlation.

 




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