A study of mean glandular dose during diagnostic mammography in Malaysia and some of the factors affecting it.

The primary objective of this study was to determine the mean glandular dose (MGD) during diagnostic mammography in Malaysia. The secondary objective was to evaluate some of the factors affecting MGD. A survey of standard MGD was performed, based upon quality control records for the period October 1999 to August 2001. This covered 30 mammography units from 9 manufacturers. MGD was also measured for a series of patients attending mammography examinations at three other mammography units. MGD per film was estimated from recorded radiographic factors, the compressed breast thickness (CBT) and X-ray unit calibration data. MGD per woman was calculated by summing the MGDs for all films, and averaging it over both breasts. 300 women drawn equally from three major ethnic groups, namely Malay, Chinese and Indian, took part in the study. The difference of MGD per woman between ethnic groups was tested for significance using non-parametric Kruskal-Wallis and median tests. The factors affecting MGD per woman were tested for significance using a multivariate analysis of variance. The MGD for the phantom was 1.23 mGy (range 0.22-2.39 mGy) while the mean patient based MGD per film was 1.54 mGy and 1.82 mGy for the craniocaudal and mediolateral oblique views, respectively. The mean MGD per woman was 3.37 mGy. It was also found that there is no significant difference in MGD per woman among the ethnic groups (p>0.05, Kruskal-Wallis test). However, on the multivariate test two factors, namely half value layer of the X-ray beam and (CBT), had a significant effect on MGD per woman (p<0.05). No significant relationships were seen between MGD per woman with respect to ethnicity, body mass index or age.