Evaluation of risks of cardiovascular disease from radiation exposure linked to computed tomography scans in the UK.

Epidemiological studies of patient populations have shown that high doses of radiation increase risks of cardiovascular disease (CVD). Results from a recent meta-analysis of 93 epidemiological studies covering a wide range of doses provided evidence of a causal association between radiation exposure and CVD, and indicated excess relative risk per Gy for maximum dose below 500 mGy or delivered at low dose rates. These doses cover the range of organ doses expected from multiple diagnostic computed tomography (CT) scans. Dose-effect factors for the excess absolute risk of mortality from CVD following radiation exposure were derived from the meta-analysis. The present study uses these factors to estimate excess risks of mortality for various types of CVD, including cerebrovascular disease (CeVD), from CT scans of the body and head, assuming that the meta-analytic factors were accurate and represented a causal relationship. Estimates are based on cumulative doses to the heart and brain from CT scans performed on 105 574 patients on 12 CT scanners over a period of 5½ years. The results suggest that the excess number of deaths from CeVD could be 7 or 26 per 100 000 patients depending whether threshold brain doses of 200 mGy or 50 mGy, respectively are assumed. These results could have implications for head CT scans. However, the results rely on the validity of risk factors derived in the meta-analysis informing this assessment and which include significant uncertainties. Further incidence studies should provide better information on risk factors and dose thresholds, particularly for CeVD following head CT scans.