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Radiation Risks Potentially Associated with Low-Dose CT Screening of Adult Smokers for Lung Cancer¹

¹ From the Center for Radiological Research, Columbia University, 630 W 168th St, New York, NY 10032. Received June 4, 2003; revision requested August 14; revision received September 16; accepted October 22. Supported by U.S. Department of Energy Low-Dose Radiation Research Program grants DE-FG-02–01ER6326 and DE-FG-02–98ER62686, and by National Institutes of Health grant RR-11623. Address correspondence to the author (e-mail: djb3@columbia.edu).

View larger version (28K): [in a new window]   Figure 1. Graph shows estimated excess relative risks for respiratory cancer (trachea, bronchus, and lung) and for all solid tumors in atomic bomb survivors exposed to a radiation dose of 50 mSv, according to age at exposure (15). Unlike the estimated relative risks for most solid cancers, that for respiratory cancer does not show evidence of decreasing with increasing age at exposure, though the mechanisms underlying this observation are not yet clear.

View larger version (26K): [in a new window]   Figure 2. Graph shows estimated excess cancer mortality by age at exposure in a stationary population that has U.S. mortality rates and that is exposed to a radiation dose of 50 mSv (16). Estimates are shown for respiratory cancers, digestive cancers, and female breast cancers. Note the different age dependence for lung cancer incidence.

View larger version (32K): [in a new window]   Figure 3. Graph shows estimated age-dependent risks, RCT, of lung cancer associated with the radiation from a single low-dose CT lung examination. The risks decrease with age at exposure because of the decreasing background lung cancer risk. Risks were estimated by using a lung radiation dose of 5.2 mSv; risks for other doses can be proportionately scaled according to the dose.

View larger version (34K): [in a new window]   Figure 4. Graph shows estimated risks, RCT, of lung cancer associated with the radiation from annual low-dose CT lung screening, as a function of the age at which annual CT screening commences. Annual examinations are assumed to commence at the specified age and continue until age 75. The risks decrease with age, both because the risks of examination decrease (Fig 3) and because fewer examinations take place. Estimated 95% CIs are approximately a factor of 3 in both directions. Risks were estimated by using a lung dose of 5.2 mSv; risks for other doses can be proportionately scaled according to the dose.

View larger version (36K): [in a new window]   Figure 5. Graph shows predicted numbers of lung cancers associated with the radiation from annual low-dose CT lung examinations in the current U.S. population. The ordering of these population risks is different from that of the individual risks (Figs 3, 4) because of the different sizes of the four subpopulations (see Table 3). Numbers are based on the assumption that 50% of all smokers and former smokers receive annual low-dose CT examinations, beginning at the specified age (or their current age, whichever is greater) and continuing until age 75. Estimated 95% CIs are approximately a factor of 3 in either direction. These results can be linearly scaled for different doses, different compliance rates, and, approximately in North American and Western European populations, different numbers in the four smoking categories.