See related research article by Eisenberg and colleagues, page 430 studies show that multiple procedures in an individual can result in a cumulative exposure that approaches or exceeds the level for which there is reasonably good epidemiologic evidence of an increased risk of cancer (ie, cumulative dose> 50 mSv). 7 It is through multiple exposures that rather insignificant risks on an individual level can become significant for a particular patient. The study by Eisenberg and colleagues shows a positive dose–response relation for radiation exposure and cancer risk at cumulative doses for which there is little previous epidemiologic evidence of increased cancer risk (ie, cumulative dose< 50 mSv). 5 Despite the demonstrated risk, only a few of the cancers diagnosed in their study were likely a direct result of exposure to radiation from the medical imaging. For example, if we consider a lifetime risk of cancer of about 2.5% for every 1000-mSv dose among individuals between the ages of 40 and 60, we would expect one new cancer for every 2000 patients receiving a 20-mSv dose that is directly attributable to the radiation exposure from the medical procedure. 9 Many of the patients in the study by Eisenberg and colleagues received a dose in this range. However, such estimates are theoretical, based on extrapolations of risk at higher doses (assuming a linear projection of risk). Although the risk of cancer at this exposure level seems to be relatively small, the fact that a large number of individuals are undergoing multiple procedures does pose a potential risk at the population level. The current wisdom for minimizing the risk to the patient is to adopt the ALARA (as low as reasonably achievable) principle. 10 This principle can be realized in a number of ways. The first is through technological innovations, which may provide means of producing suitable images with reduced levels of radiation exposure. For example, innovations in cardiac CT technology over the past five years have resulted in a decrease in the minimum achievable dose from 10–16 mSv to as low as 1–3 mSv. Another way is for physicians to optimize their technique or protocols. As with other health risks, the best strategy may be prevention. This could mean referring the patient for a procedure that involves lower or no radiation exposure or, in some circumstances, avoiding the procedure altogether. Prevention may become of prime importance in situations where a patient has undergone or is expected to undergo a series of tests or procedures with moderate to high levels of exposure to radiation. The standard by which one chooses to avoid a procedure or suggest an alternative may depend on whether the procedure is indicated for the purpose of improving prognosis or for diagnosis only. For example, in the case of primary angioplasty in acute myocardial infarction, the immediate and substantial improvement in prognosis may sufficiently outweigh the comparatively small risk of cancer in the long term. Communication between the referring physician and the radiologist or specialist should be encouraged in an effort to find the optimal diagnostic or therapeutic strategy for the patient.

It is not uncommon for a patient to be re ferred for a variety of medical imaging tests and procedures by different physicians. It can be difficult, therefore, for an individual physician to keep track of the patient’s cumulative exposure (assuming information about the radiation dose is available for each procedure—it is often not). The implementation of a strategy to track radiation doses may help physicians and patients stay aware of the cumulative exposure. Health care and nuclear industries currently use such strategies …