Comparison of the European and Nordic protocols on dosimetry in mammography involving a standard phantom

The purpose of this work was to implement the European Protocol on Dosimetry in Mammography in Sweden. The standard average glandular dose, AGD, was measured on 32 mammography units in southern Sweden, according to the European protocol as well as to the Nordic protocol. The most important difference is that the European protocol evaluates the half value layer, HVL, of the X ray beam with the compression paddle present, while it is absent in the Nordic protocol. This results in considerably higher HVL values from the European protocol and thus to higher conversion factors for the calculation of the standard AGD. When the European protocol is used instead of the Nordic protocol the standard AGD is increased by 5 +/- 2% (total variation 0-9%) at clinical settings and by 9 +/- 3% (4-17%) at a standardised net optical density of 1.00. These results should be considered in quality control programmes and optimisation procedures as well as in interpretation of trends and in future legislation programmes.