The potential risks from exposure to ionizing radiation during cardiac computed tomography angiography (CCTA) have led many to question the role of this technique.The Prospective Multicenter StudyOn Radiation Dose Estimates Of Cardiac CT Angiography In Daily PracticeI (PROTECTION I) was an observational study of estimated radiation dose in 1965 patients undergoing CCTA over an 11 month period.

The median dose-length product (DLP) of 1965 CCTA examinations performed at 50 study sites was 885mGy per cm, which corresponds to an estimated radiation dose of 12mSv. This equates to 1.2 times the dose of an abdominal CT study, or 600 chest X-rays. Moreover, a large variability in DLP was noted between study sites, with a range of 331-2146 mGy per cm.

The authors conclude that the median radiation doses from CCTA differ significantly between individual centres and CT systems. The dose of radiation received can be difficult to estimate, and the study does not look at any links between the radiation dose received and cancer, but one important finding was that strategies known to reduce radiation dose were not implemented. Results from PROTECTION 2 and 3, due later this year, will determine whether image quality can be maintained with lower doses of radiation.

• Hausleiter J, Meyer T, Hermann F, et al. Estimated radiation dose associated with cardiac CT angiography. JAMA 2009; 301:500-507.
• Einstein AJ. Radiation protection of patients undergoing cardiac computed tomographic angiography. JAMA 2009; 301: 545-547.