Volume of screening mammography and performance in the Quebec population-based Breast Cancer Screening Program

Background

In the Quebec Breast Cancer Screening Program (Programme québécois de dépistage du cancer du sein PQDCS]), radiologists'' and facilities'' volumes of screening mammography vary considerably. We examined the relation of screening-mammography volume to rates of breast cancer detection and false-positive readings in the PQDCS.

Methods

The study population included 307 314 asymptomatic women aged 50–69 years screened during 1998–2000. Breast cancer detection rates were analyzed by comparing all women with screening-detected breast cancer (n = 1709) and a 10% random sample of those without (n = 30 560). False-positive rates were analyzed by comparing the 3159 women with false-positive readings and the 27 401 others in the 10% random sample. Characteristics of participants, radiologists and facilities were obtained from the PQDCS information system. Data were analyzed by means of logistic regression.

Results

The rate of breast cancer detection appeared to be unrelated to the radiologist''s screening-mammography volume but increased with the facility''s screening-mammography volume. The breast cancer detection rate ratio for facilities performing 4000 or more screenings per year, compared with those performing fewer than 2000, was 1.28 (95% confidence interval CI] 1.07–1.52). In contrast, the frequency of false-positive readings was unrelated to the facility''s screening volume but was inversely related to the radiologist''s screening volume: the rate ratio for readers of 1500 or more screenings per year compared with those reading fewer than 250 was 0.53 (95% CI 0.35–0.79).

Interpretation

Radiologists'' and facilities'' caseloads showed independent and complementary associations with performance of screening mammography in the PQDCS. Radiologists who worked in larger facilities and read more screening mammograms had higher breast cancer detection rates while maintaining lower false-positive rates.Caseload of health care providers and organizations has been linked with performance.^1,2,3,4 Providers with larger volumes of patients or procedures have often been shown to have better outcomes.^2,5 However, a recent comprehensive review of the literature underlined the methodologic limitations of published studies, especially poor adjustment for case mix and failure to account for characteristics of providers and organizations simultaneously.⁶The population-based Quebec Breast Cancer Screening Program (Programme québécois de dépistage du cancer du sein PQDCS]), launched in 1998, follows the North American standard of a minimum annual reading volume of 480 mammographic examinations (diagnostic and screening combined) for each collaborating radiologist.⁷ In addition, facilities in urban areas have to perform at least 4000 diagnostic or screening examinations each year to be eligible for the program.⁸ However, there is a large variability in radiologists'' and facilities'' volumes of screening examinations.The objective of our study was to assess whether differences in screening volume were associated with rates of breast cancer detection and of false-positive readings. We examined the separate and combined effects of radiologists'' and facilities'' screening-mammography volumes.