ORIGINAL ARTICLECancer detection and mammogram volume of radiologists in a population-based screening programme
Introduction
The efficacy of mammography screening in reducing breast cancer mortality has previously been shown in both randomised trials and service studies,1, 2, 3, 4 despite controversies regarding effect size and target age-groups.5, 6, 7 Randomised trials have shown that a 30% reduction in breast cancer mortality is achievable in women aged 50–69 years.3 BreastScreen New South Wales (BSNSW) is a population-based mammography screening programme that targets women aged 50–69 years. Women who attend BSNSW undergo bilateral two-view mammography, with all films read independently by two radiologists. Where there is disagreement between the two radiologists regarding a recall to assessment, the final recommendation is based on either the consensus opinion of both radiologists, or the recommendation of a third radiologist.
Radiologists in NSW contract their services to the State-funded screening programme with agreement to comply with established national accreditation standards and requirements.8, 9 Currently, the minimum number of reads per year required of radiologists in BSNSW is 2000,8 and was derived from considerations of standards in the United States (480 mammograms per year),10 the United Kingdom (5000 mammograms per year),11 and Canada (2000 mammograms per year).12
The aim of this study is to investigate the relationship between the number of mammograms read by radiologists and the breast cancer detection rate, and to determine if a cut-off point exists where the relationship changes significantly. This information is relevant to inform programme standards of minimum mammogram reads per radiologist for optimal cancer detection.
Section snippets
Data
The number of mammograms read for all incident screens and the number of cancers detected (invasive and ductal carcinoma in situ) were obtained for 134 radiologists contracted by BreastScreen NSW for the period January 2000 to December 2001 for all women (⩾40 years) attending 9 of the 10 Screening and Assessment Services (SAS) in New South Wales. One SAS was unable to participate in the study; this SAS conducted 11,055 incident screens, or 1.2% of all incident screens. Prevalent screens refer to
Results
Individual cancer detection rates ranged from 0 to 141 per 10,000 mammograms, however large variation in cancer detection was evident for low numbers of annual reads (Fig. 1). The mean cancer detection rate was 38.6 per 10,000 (95% confidence interval of 34.9–42.3) including all mammograms, and 42.0 per 10,000 (95% CI 39.4–44.6) excluding reader volumes of less than 500. Cancer detection rates increased with number of mammograms read, and peaked in quintile 2 (270–1459 mammograms per
Discussion
This study investigated the association between the number of mammograms read by radiologists in the screening programme and cancer detection rates for incident screens, using routinely collected mammography data from NSW (2000–2001). Cancer detection rates increased with the number of mammograms read, reaching a plateau at approximately 1300 mammograms per year. Poisson regression models of cancer detection rates for increasing cut-points of the number of mammograms read showed that cancer
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