To put the risk of radiation in perspective, in 2002 malignant neoplasms caused the death of 557,271 people (of a total of 2,443,387 deaths) (12) in the U.S. It is unclear how many of these malignant neoplasms were related to radiation exposure. High doses of radiation are clearly linked to immediate and delayed effects (13), whereas the effects of long-term exposure to very low levels of radiation, as used in diagnostic procedures, remain highly controversial. For example, no additional risk of cancer was found in populations exposed to higher levels of background radiation (14- 15) or among individuals (such as airline pilots) receiving relatively high occupational exposures (16- 17). Despite such data, various advisory bodies used the conservative assumption that no level of radiation is without excess risk, that is, the zero threshold hypothesis. To estimate the practically immeasurable risk from low-level radiation, various mathematical models are required to extrapolate dose-risk data from highly exposed populations. Currently, a linear relationship between dose and risk is used in the risk model for low-level exposures. The National Council on Radiation Protection and Measurements (NCRP) thus recommends a risk factor of 5 × 10−2 Sv−1 for lifetime cancer mortality for the general population (18). Conceptually, this means that if a randomly selected population of 100 people each received an effective dose (ED; see the Appendix for approaches to calculating the radiation burden) of 1 Sv (100 rem), which is equivalent to a uniform whole-body absorbed dose of 1 Gy (100 rad) of sparsely ionizing radiation (such as diagnostic X-rays), five additional fatal cancers would ensue over the balance of the lifetimes of the irradiated individuals. The BEIR V Committee (19) endorsed a somewhat-higher risk factor of 7.9 × 10−2 Sv−1. Importantly, as lifetime risk factors for the general population, these represent age- and gender-averaged values. However, in the patient population of Coles et al. (11), the population was skewed toward older individuals, with a mean age of approximately 62 years. For such an older population, the risk factor for lifetime cancer mortality is less than one-half of that for the general population and less than one-third of that for a younger population (i.e., younger than 55 years of age) (20). The use of general-population (i.e., age-averaged) risk factors will therefore overestimate the actual radiogenic risk to older patients, that is, patients typically being evaluated for coronary artery disease.