Big cuts in appendicitis CT scan dose possible, study suggests

It should be possible to reduce radiation dose levels by as much as 50% in CT appendicitis scans without seriously sacrificing accuracy, a study presented Tuesday by Duke University researchers concluded. 

Using a process that added simulated noise from reduced dose to actual abdominal images, the researchers compared the noisy images to the actuals and looked for reader agreement. They found that the simulated reductions of 25% and 50% were acceptable, but that a 75% reduction decreased confidence in the accuracy of the interpretation.

The study covered abdominal images from 100 patients. A noise introduction tool was used to create images with simulated drops of 25%, 50%, and 75% in the mA levels. Those images and the actuals were then randomized and read by three fellows and rated for diagnostic confidence, the ability to identify the appendix, and whether it was normal.

For all patients, agreement between readers on identification of the appendix on the original and the three reduced-dose scans was reasonably high. Means were 86%, 81%, 77%, and 77%, respectively. For patients without appendicitis, agreement on whether the appendix was normal was even higher; means were 91%, 91%, 90%, and 84%. For patients with appendicitis, mean agreement was highest at 100%, 97%, 100%, and 100%.

The researchers also evaluated the confidence levels of the readers, said Dr. Erik Paulson, who presented the study.

Using the actual images, most readers had confidence levels of 4 and 5, and even with a 25% dose reduction, the confidence level was “excellent,” Paulson said. When reducing dose to the 50% level, more 2 and 3 ratings emerged, and at 75% reduction, a loss in confidence was identified.

Paulson said there was excellent agreement around identification of the appendix at low dose, the presence of abnormalities, and the presence of disease, and that the accuracy was maintained up to a 50% dose reduction. He cautioned, however, that the simulation may overstate the actual amount of dose reduction.

“I think a reasonable take-home message is that even using a routine CT technique, reducing dose is warranted in patients with suspected appendicitis,” he said.

In the question-and-answer session, Paulson was asked how low dose could go in appendicitis scans.

“I wouldn’t be prepared to drop by 75%; I think that would be too much. But there have been several studies that with mA of 10 or 30-almost CT flouro mA-one can make a diagnosis of appendicitis,” he said.