Comparative study of dose values and image quality in mammography in the area of Madrid.

Dose values and image quality in mammography resulting from a study carried out in the area of Madrid during 1990-1991 are presented in a two-part sequence. In this paper are reported the values of air kerma and mean glandular dose per film estimated at 14 centres by means of the Leeds TOR(MAX) mammographic phantom and from patient samples. The results obtained from patient measurements allow us to deduce that the TOR(MAX) phantom assembly used (4.5 cm thick) is equivalent to an average 5 cm thick compressed breast from the population in the area of Madrid. Approximately 75% of the air kerma values resulting from phantom estimations are below 6.6 and 12.2 mGy for X-ray units with and without grid, respectively. The mean glandular doses per film for 75% of the units with and without grid are below 1.5 and 1.7 mGy, respectively. The results showed that the higher values of both air kerma and mean glandular dose obtained for the units without grid result from the use of slow speed recording systems. On the other hand, the quality control programme carried out shows important faults in the performance of the X-ray units which have an important impact on both dose and image quality. Finally, the third quartile values of the air kerma and mean glandular dose per film (10.4 and 1.7 mGy, respectively), deduced by considering all the units (with and without grid), are proposed to be the reference values of the mammographic examinations during the aforementioned period. In a second paper, the image quality is analysed by using the same Leeds TOR(MAX) phantom. Results for each test object included in the phantom are discussed as a function of the X-ray unit characteristics. Subsequently, the phantom images obtained with each X-ray system are scored and the resulting values are compared with the corresponding dose values, so that the dose-image quality relationship for each unit is obtained.