No Cancer Detection Decrease in Mammograms Over Time

Reading mammograms for longer periods of time did not reduce cancer detection, but increased overall performance.

A recent study found there was no reduction in accuracy over time of medical staff who analyze mammogram scans.

According to the study, published in JAMA, researchers analyzed whether detection rates declined near the end of each batch of mammogram readings indicating a phenomenon called the vigilance decrement.

Mammograms have a lot of tissue that overlaps, which can make cancer detection difficult. Researchers found that cancer detection rates did not vary throughout each of the 35 readings per batch.

"We found no reduction in performance or vigilance decrement at all. In fact, we found the opposite of what we were expecting -- breast screening readers seemed to get 'into the zone' and their performance improved with time on task,” said Sian Taylor-Phillips, MPhys, PhD. “They recalled fewer women for further tests as they got nearer the end of the batch while cancer detection rates stayed constant."

Typically, 2 trained readers examined each mammogram for signs of cancer. According to the study, both readers examine the mammograms in the same order so in case there is a vigilance decrement, the vigilance will be low for both readers.

A randomized controlled study was conducted that incorporated 1.2 million mammograms. Researchers did not notice any effect on cancer detection rate over time; however, in a post-hoc analysis, researchers found that performance improved with time.

Readers were able to keep accurately detecting cancer, but the number of women they asked for further tests decreased over time. When they began the task, readers recalled 6.4 women per thousand, and this number decreased to 4.6 per thousand after examining 40 mammograms in a row.

"Psychologists have been investigating a phenomenon of a drop in performance with time on a task called 'the vigilance decrement' since World War 2. In those days radar operators searched for enemy aircraft and submarines which appeared as little dots of light on a radar screen,” Dr Taylor-Phillips said. "People thought that the ability to spot the dots might go down after too much time spent on the task. Many psychology experiments have found a vigilance decrement, but most of this research has not been in a real world setting, unlike our study."

Researchers concluded that they will further their research by evaluating how performance changes over a longer session and whether time of day effects performance.