How low can you go? Tool balances pediatric CT risks & benefits

A team of radiologists has developed diagnostic reference ranges (DRRs) that allow practices to calculate reference dose ranges for abdomen and pelvis CT exams in children, according to a study published online March 19 in Radiology. The resulting doses were nearly 70 percent lower than previously published data on pediatric dose.

The retrospective study enrolled 939 patients, ages 1 day to 18 years, from Sept. 1 to Dec. 1, 2009. Pediatric radiologists applied a five-point CT image quality scale to calculate an appropriate dose range for each DRR.

“The purpose of our study was to develop DRRs and a method for an individual practice to calculate site-specific reference dose for CT scans of the abdomen or abdomen and pelvis in children that are based on body width (BW),” wrote Marilyn J. Goske, MD, from the department of radiology at Cincinnati Children’s Hospital Medical Center, and colleagues.

Patients were grouped into five BWs: < 15 cm, 15-19 cm, 20-24 cm, 25-29 cm, and ≥ 30 cm, with BW marked at the splenic vein for consistency. Among all patients, BW ranged from 10 to 45 cm. The most common indications for CT imaging were abdominal pain, right lower quadrant pain and appendicitis.

Adjusted size-specific dose estimates (SSDE) ranged from 9.6 to 16.8 mGy. Of the 106 scans selected for subjective image analysis, six were ranked nondiagnostic; five of these had an SSDE less than the 25th percentile and the sixth had a metal implant artifact.

The 75th percentile of the DRR serves as a dose ceiling facilities should strive not to exceed, while the lower limit offers a dose floor required for image quality.

Goske et al noted both progress and room for improvement in pediatric exposure. A European dose survey published in 1999 reported a CTDI of 12.5 mGy; the corresponding figure for the current study was 7.6 mGy. Canadian data on dose-length product and effective dose for 5-,10- and 15-year old patients were 8.4 mSv, 8.9 mSv and 5.9 mSv, respectively, in 2008, compared with 5.8 mSv, 6.3 mSv and 7.1 mSv, respectively, in the current study.

However, the current study was completed with CT systems that did not have the capability to perform iterative reconstruction, which could further reduce dose.

As far as CT imaging in practice, “A facility’s radiologists, technologists, and medical physicist should work together to establish reference doses and generate technique charts with reduced tube current and/or high voltage values that result in patient dose (SSDE) less than the reference dose for a given BW,” wrote Goske and colleagues.

They also explained that certain indications such as renal stone disease are likely to require reduced DRRs, while applications of increased complexity may require higher dose.