Radiation Doses and Risks in Chest Computed Tomography Examinations

Effective doses, and the corresponding risks of radiation-induced cancers, are presented for patients undergoing chest computed tomography (CT) examinations. Patient dose calculations were based on the characteristics of 16-slice CT scanner from 4 imaging equipment vendors. The dose-length product (DLP) was used to quantify the amount of radiation used to perform chest CT examinations. Values of DLP were converted into a corresponding effective dose (E) using age-dependent E/DLP conversion coefficients applicable to chest CT examinations. Calculations of effective doses were performed for a typical chest CT examination, as well as for a low-dose protocol for patients with cystic fibrosis. Effective doses were used to estimate nominal cancer risks based on data in Report VII of the Committee of the Biological Effects of Ionizing Radiation. Patient effective doses in standard chest CT examinations range from approximately 1.7 millisieverts (mSv) in newborns to approximately 5.4 mSv in adults. The effective dose to a 5-year-old patient with cystic fibrosis using a low-dose protocol is approximately 0.55 mSv, which is about a factor of four lower than a standard chest CT examination. An effective dose of 0.55 mSv for a 5-year-old patient corresponds to a nominal excess risk of carcinogenesis of approximately 1.5 cancers per 10,000 individuals, with half of these being fatal. It is concluded that patients undergoing chest CT examinations should have a benefit that exceeds the (small) radiation risk.