New diagnostic reference level for full-field digital mammography units

The diagnostic reference level (DRL) has generally been defined as the 75th percentile of the distributions of mean doses observed on a sample of standard-sized patients, but for mammography, the 95th percentile has been used. In this study, the 75th and 95th percentiles are estimated for 26 full-field digital mammography units, representing six models from four manufacturers. Systematic differences between categories of manufacture/models are investigated with respect to mean glandular dose (MGD) and figure of merit (FOM), defined as signal difference to noise ratio squared divided by the MGD. The MGDs per unit range from 0.7 to 2.1 mGy, with overall 75th and 95th percentiles of 1.4 and 2.0 mGy, respectively. The different manufacture/models show differences in both dose distributions and FOMs. As national DRL, the 95th percentile is proposed to determine which units can be accepted for use. To identify the need for optimisation, it is proposed to use the 75th percentile for the different manufacture/models, along with the FOM.