Trends in compressed breast thickness and radiation dose in breast screening mammography.

An analysis was performed of the compressed breast thickness recorded in 146 mammographic patient dose surveys each consisting of 50 or more women carried out between 1993 and 2004. The results show a steady and statistically significant increase in compressed breast thickness with time, which is also present when individual independent screening centres and equipment manufacturers are compared. This increase seems most likely to be associated with an increase in the proportion of women in the breast screening age range classified as overweight and obese, which has occurred over the same time period. The associated trends in mean glandular dose per image were calculated for the mammography units used at the time of the surveys, using the most recently published conversion factors. The increase in average radiation dose that might have been expected as a result of the increase in average compressed breast thickness was not actually found in practice, possibly because of advances in equipment design and dose optimization strategies made during the 11-year period. Other implications of an increasing average compressed breast thickness are discussed.