The first two years of digital mammographic screening in New Zealand

BreastScreen Waitemata Northland started as a new lead provider for the New Zealand breast screening service in February 2006 with a new fully digital facility and several analogue regional subsites. Some of these latter sites have subsequently been replaced by two further digital facilities, gradually changing the proportion of digital screening mammograms from 32% to 73% of our workload over 2 years, with 53,800 women screened. This was the first digital screening site in New Zealand. We have compared the results of screening with analogue and digital technology over our first 2 years, in terms of recall rates, cancer detection rates and positive predictive value, and found no overall significant difference in any of these parameters. We have found improved detection of malignant microcalcifications with digital mammography, with a similar proportion of these malignancies that were either invasive cancer or high-grade ductal carcinoma in situ as those detected with analogue technology. However, we have found better detection of nonspecific densities with analogue imaging. There is a trend towards better cancer detection with analogue than digital technology in the 64 to 69 years age group, which does not reach statistical significance.