Medically unnecessary multiphase CT exams are common and account for a substantial amount of excess radiation exposure, according to a study published in the November issue of Journal of the American College of Radiology, which led the authors to call for an end to routine use of “one-size-fits-all” multiphase protocols for abdominal and pelvis exams.

“The motivation for this study was the anecdotal observation that a large portion of CT studies submitted to our tertiary center for reinterpretation were performed with multiphase scan protocols that were not appropriate for the clinical indication,” wrote Kristie M. Guite, MD, of the department of radiology at University of Wisconsin, Madison, and colleagues.

The use of multiphase studies when a single or lesser number of phases would suffice represents an “important but potentially overlooked” strategy for reducing radiation, according to Guite et al.

The researchers hypothesized that the extra CT phases result in excess radiation and tested the hypothesis via retrospective analysis of 500 abdominal and pelvis studies submitted for tertiary review. Guite and colleagues assessed the studies for appropriateness based on the clinical indication and American College of Radiology (ACR) Appropriateness Criteria and calculated per phase and total radiation effective dose.

They found that 307 of the 500 patients underwent multiphase CT studies, and 86 percent of this group had at least one unindicated phase. In total, 35.8 percent of all phases were unindicated, with delayed phase imaging accounting for the majority of the unindicated phases.

Patients who underwent excess phases received more than double the mean effective dose per patient than those who received the correct number of phases, at 36.5 mSv and 17.5 mSv, respectively. The researchers calculated that unindicated phases accounted for 33.3 percent of total effective dose.

Patients 50 years old or older and those being evaluated for malignancies were more likely to receive excess effective doses.

Guite and colleagues calculated a mean effective dose in study population of 25.8 mSv, which could have been reduced to 17.9 mSv if patients had received only phases indicated by ACR appropriateness criteria. “This suggests that the high radiation doses seen in this population (and potentially throughout the country) are correctable with simple changes in practice,” they wrote.

The study design did not allow the researchers to determine the reason for the inappropriate multiphase studies. However, they surmised “a lack of focus on performing protocols tailored for the individual patient and clinical indication is the predominant factor, with most patients being prospectively scanned to reduce callbacks.”

It will become increasingly difficult to justify multiphase exams as radiation exposure becomes linked with healthcare quality, noted the researchers, adding, “The results of this study make it clear that there is substantial room for improvement.”

Guite and colleagues suggested that widespread adoption of individual scan protocoling guided by appropriateness criteria could nearly eliminate excess radiation caused by unnecessary multiphase scanning.