High CCTA radiation exposure underscores need for better user education

Results from an international trial involving 44 sites have confirmed that the routine clinical use of cardiac CT angiography exposes patients to large amounts of ionizing radiation. The amount of radiation exposure varies considerably, suggesting that users have not uniformly adopted dose-reducing imaging strategies, according to a study presented Monday at the 2008 American College of Cardiology meeting in Chicago.

An interim analysis from the Prospective Multicenter Study on Radiation Dose Estimates of Cardiac CT Angiography in Daily Practice (Protection I) found that patients undergoing cardiac CT scans received an estimated average dose of 17.1 mSv. The estimate was based on a mean scan length of 144 mm (±11 mm) and a CTDI_VOL, a measure of radiation dose specifically derived from multislice CT imaging, of 65.9 mGy (±69.3 mGy).

Radiation dose estimates differed significantly depending on site and equipment model, said Dr. Joerg Hausleiter from the German Central Heart Hospital in Munich, Germany.

Mean doses ranged from 8.5 mSV to 43.8 mSV among the participating sites. The mean exposure from specific, though unnamed, 64-slice scanners ranged from 11.8 mSv (±4.5 mSv) to 25.2 mSv (±12.1 mSv).

Overall, ECG-correlated tube current modulation was used to reduce exposure in 82% of the exams. Application of the strategy resulted in an average 21% reduction in the estimated dose, according to Hausleiter.

The Protection I trial was designed to examine the extent to which participating sites used tube current reduction and dose-saving algorithms. It also measured effect of their use on patient radiation exposure.

Collaborators, including Dr. Stephan Achenbach at the University of Erlangen in Germany and medical physicist Cynthia H. McCollough, Ph.D., of the Mayo Clinic in Rochester, MN, found that the radiation dose fell an average of 51% when the tube current was reduced from 120 kV to 100 kV. A 67% dose reduction was realized when spiral data acquisition, based on sequential scan algorithms, was applied. The study found, however, that only 6% of the sites used the tube current reduction strategies. Only 2% had adopted sequential scan algorithms.

The findings were based on 1729 CCTA procedures performed consecutively for a one-month period on various types of 64-slice CT equipment at participating sites. Enrollment ended in December 2007. About 83% of the procedures involved coronary artery assessment.

The results called the investigators' attention to the need for better education worldwide to promote a wider adoption of dose-saving algorithms for cardiac CTA. More types of dose-saving algorithms also need to be built into commercial cardiac CTA systems, according to the investigators.

For more information from the Diagnostic Imaging archives:

Study assuages cardiac CT radiation worries

CT vendors renew emphasis on safety and speed

Researchers stress need for better dose reduction strategies