Determination of average glandular dose with modern mammography units for two large groups of patients

Abstract

Until recently, for mammography Mo anode-Mo filter x-ray tube assemblies were almost exclusively used. Modern mammography units provide the possibility to employ a variety of anode-filter combinations with the aim of adapting the x-ray spectrum to compressed breast thickness and composition. The present contribution provides information on the radiation exposure of two large groups of patients (one of 1678 and one of 945 women) who were mammographed with modern x-ray equipment, and on the dosimetry necessary for the evaluation. For dosimetric purposes spectral information is essential. X-ray spectra have been determined for various anode-filter combinations from measurements with a Ge detector. Based on these spectra, conversion factors from air kerma free in air to average glandular dose (g factors) have been calculated for different anode-filter combinations, compressed breast thickness ranging from 2 to 9 cm and breast compositions varying from 0 to 100% glandular tissue. Determinations of various quantities, including entrance surface air kerma (ESAK), tube output, tube loading (TL), fraction of glandular tissue (FGL) and compressed breast thickness, were made during actual mammography. Average glandular dose (AGD) was determined using g factors corrected for tissue composition as well as g values for standard breast composition, i.e. 50% adipose tissue and 50% glandular tissue by mass. It is shown that, on average, the influence of the actual breast composition causes variations of the order of about 15%. For group 1 and group 2, the mean values of average glandular dose (using g factors corrected for tissue composition) were 1.59 and 2.07 mGy respectively. The number of exposures per woman was on average 3.4 and 3.6 respectively. The mean value of compressed breast thickness was 55.9 and 50.8 mm respectively. The mean age of group 1 was 53.6 years (for group 2 the age was not recorded). The fraction by mass of glandular tissue FGL decrease with increasing compressed breast thickness and age of patient (from 75% at 25 mm to 20% at 80 mm, and from 65% at 20 years to 30% at 75 years). For a medium-sized breast, i.e. a compressed breast thickness of 55 mm, FGL is about 35%, indicating that the standard mix (FGL = 50%) might need some modification, particularly because of additional evidence from another investigation with similar results on FGL.

Glandularity and mean glandular dose determined for individual women at four regional breast cancer screening units in The Netherlands

“…The glandularity averaged over all four centres is 32%, which is reasonably close to the values of 35% and 43% found by Klein et al (1997), but considerably smaller than the average glandularity assumed in most dosimetry protocols, i.e. 50% glandularity, e.g.…”

“…The compressed breast thickness averaged over all participating women is approximately 5.82 cm. This is slightly higher than the values of 5.59 and 5.08 cm found for two groups of patients by Klein et al (1997), but in the range of values for compressed breast thickness found by Eklund et al (1993). The standard deviations of compressed breast thickness found by Klein et al (1997) Mean glandular dose values are given for each unit in table 2.…”

“…This is slightly higher than the values of 5.59 and 5.08 cm found for two groups of patients by Klein et al (1997), but in the range of values for compressed breast thickness found by Eklund et al (1993). The standard deviations of compressed breast thickness found by Klein et al (1997) Mean glandular dose values are given for each unit in table 2. The largest average glandularity is found for the participants in Amsterdam, whereas the compressed breast thickness is smallest at this unit (table 2).…”

“…In addition, the tests according to Press et al (1987) of the skewness of the distributions of the compressed breast thickness and of the mean glandular dose as shown in figures 3 45-49 years participated compared to that in the other centres (figure 2) and a relatively large number of women with thinner compressed breasts were observed ( figure 3). An increasing glandularity with decreasing age has usually been observed (Klein et al 1997, Dance et al 2000, as well as an increasing glandularity with decreasing breast thickness (Zoetelief et al 1989). The relatively low value for the average glandularity in Heerenveen might be attributed to the relatively larger number of women with larger compressed breast thickness (figure 3) and the relatively higher ages (figure 2) of the participating women compared to the other centres.…”

The Normal Types of Ultrasound Breast Morphology (Glandular Tissue And Fat Lobules) among Women of Different Age Groups in Golden Horses Health Sanctuary

“…This decrement is due to an increase in the proportion of adipose tissue in the breast. This trend is similar to that reported [14][15][16] for German, British, and Jamaican studies, respectively. Interestingly, we found that the greatest rate of change occurs after the age of 50 years whereas, [15,17] reported that the greatest rate of change occurs between the ages of 45 and 55 years.…”