Rasika Rajapakshe PhD, Presenter: Nothing to Disclose

To characterize the distribution of compressed breast thickness within the Screening Mammography Program of British Columbia.

SMPBC has been providing population breast screening to women in the province of British Columbia since 1988. Since inception, all mammography machines within the program have been tested annually by physicists. In order to characterize the radiation detriment to the screening population, the mean glandular dose for each screening site has always been estimated for a 4.2 cm Lucite phantom (4.5 cm 50/50 equivalent) as recommended by the AAPM report No 29 (Report of the Task Group No 7 , AAPM 1990). However, the applicability of 4.5 cm thickness as the representative compressed breast thickness has never been validated for the SMPBC. Therefore, this study was undertaken to estimate the average compressed breast thickness of a random sample of 50 women each from the screening sites within the SMPBC. Volunteer radiation technologists from all 39 SMPBC screening sites were asked to record the techniques factors (including the compressed breast thickness) of the four bilateral mammograms of 50 consecutive women who underwent screening in April of 2007. Volunteers from only 31 sites responded to this request (80% of the sites). Data collected were then analyzed statistically for each site as well as collectively. The compressed breast thickness reported by every mammography unit within the SMPBC is verified to be within +/- 0.5 cm as part of the annual physicist testing.  

The average compressed breast thickness for the 31 sites (population average) was calculated to be 5.4 cm (standard deviation of 1.3 cm). The average compressed breast thickness for each site ranged from 4.4 cm (standard deviation of 1.4 cm) to 6.5 cm (standard deviation of 1.2 cm).

The 4.5 cm represents the lowest average compressed breast thickness within the SMPBC screening sites. It was found that 5.5 cm would be a better representative value for the average compressed breast thickness within the SMPBC for the estimation of mean glandular dose.  

Phantom thickness of 5.5 cm is found to be a better representative value than the universally accepted thickness of 4.5 cm for the estimation of mean glandular dose within the SMPBC.

Rajapakshe, R, Distribution of Compressed Breast Thickness within the Screening Mammography Program of British Columbia (SMPBC).  Radiological Society of North America 2009 Scientific Assembly and Annual Meeting, November 29 - December 4, 2009 ,Chicago IL. http://archive.rsna.org/2009/8013495.html