Mismatched breast, detector size increase patient radiation dose

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A mismatch in breast-detector sizes causes significantly greater radiation dose for patients with large breasts imaged in a small detector, according to a study published in the January 2014 issue of Academic Radiology.

Mammography aims to minimize the exam’s radiation dose while identifying and evaluating breast cancer and breast disease. Digital mammography is comprised of detectors that come in four basic designs: phosphor-charge coupled devices (CCD), photostimulable phosphors, flat panel phosphors, and selenium flat panel imagers.

The study’s lead author, Catherine L. Wells, MD, PhD, of the Albany Medical Center South Clinical Campus in New York, and colleagues wrote, “CCD, the most common type of detector, provides high spatial resolution; however, because of manufacturing constraints CCD-type mammographic detectors are available only in preset sizes (small and large detectors). When using mammographic detectors of different sizes, it is often difficult to match patient breast size to optimal detector size.” Thus, Wells and colleagues created a study to determine if increased radiation exposure is a result of a mismatch between breast size and optimal detector size.

The study’s population was comprised of 864 patients who underwent screening and diagnostic mammography during a six-week period in November to December of 2009. The researchers gathered data for breast size (large or small), detector size used, number of views obtained, mean glandular dose (MGD) per breast, and patient waiting time. The average MGD and average waiting time were calculated for imaging performed on appropriately matched or mismatched breast/detector size pairs.  

Results indicated that screening mammography patients with large breasts who were imaged on a small detector received a significantly higher radiation dose and greater number of views than the optimally matched breast-detector pairs. Diagnostic mammography patients with large breasts who were imaged on a small detector received a higher radiation dose than the optimally matched breast-detector pairs but did not have an increased number of views. The researchers found that waiting times were longer for a large detector.

“Departmental pressure to maintain patient throughput and minimize waiting time may inadvertently be associated with increased radiation exposure if efforts are not made to minimize mismatches between breast and detector sizes, such as scheduling patients according to their bra size. We recommend that detector size should be matched to breast size whenever possible but particularly for larger breasted patients,” wrote the study’s authors.