Chest
Special FeaturesChest ImagingRadiation and Chest CT Scan Examinations: What Do We Know?
Section snippets
Radiation Effects of Chest CT Scans on the Individual Patient
Pioneers of radiation science discovered that ionizing radiation from x-rays causes damaging physical effects.13 Electrons are liberated when x-rays traverse living cells. Free electrons may mutate DNA directly or ionize water molecules to form harmful reactive oxygen species. Most damage is readily repaired, though persistent DNA damage may lead to cellular loss of function, necrosis, or malignancy.8, 12, 14
The term stochastic effect refers to tissue damage from low doses of radiation that is
Discussing Risks With Patients
Given the complex nature of the subject, it can be challenging to discuss the radiation risks of CT scanning with patients. It may be important to avoid citing numeric values for which patients have no frame of reference. A comparison with natural background radiation exposure may be better understood. In 1 year, individuals receive slightly less than one-half the dose associated with a routine chest CT scan from background sources, including cosmic radiation and radon gas (3 mSv).19 Another
Public Health Effects of Chest CT Scans
CT scanning has revolutionized the management of many diseases.5, 11 Its cost, availability, convenience, and versatility have made it one of the most used and fastest growing imaging technologies.11, 15 In 1993, about 18 million CT scans were performed in the United States, and in 2007, this number had increased to > 70 million.5, 7 During this period, CT scan utilization grew at 10 times the rate of US population growth.14
Diseases of the chest are major public health concerns, and advances in
Efforts to Reduce Radiation Dose
Efforts have been made to decrease CT scan-related radiation dose on the population and individual levels.9, 11, 28 Dose reduction strategies are summarized in Table 2.
Population-Wide Dose Reduction Initiatives
In the United States, medical radiation has replaced background radiation as the primary source of population-wide exposure.18, 29 The threshold for ordering CT scan has lowered even in younger, healthier patients for whom risks may outweigh benefits.5, 15, 30 Risk-benefit analyses are difficult to perform, and available decision aids often are underused in practice.11
It has been estimated that 26% to 44% of CT scans are ordered inappropriately.5, 11,15, 37 To counter this, appropriateness
Reducing Radiation Dose From Individual Studies
Reducing the dose administered during each study decreases individual radiation burden from CT scan. Evidence-based decision-making identifies patients for whom a CT scan study would provide clear net benefit and situations in which imaging tools that do not deliver radiation (eg, MRI, ultrasonography) are appropriate.5, 15 Once the decision for a CT scan has been made, it is important to optimize technical parameters to minimize risk and maximize diagnostic utility. Dose reduction strategies
Radiation, Cancer Risk, and Specific Chest CT Scan Modalities
Dose estimates from various chest CT scan studies are summarized in Table 4.
Conclusions
Even if single CT scans increase the individual risk of malignancy minutely, expanding use amplifies population-wide risk.5, 8,14, 15 There is still scientific uncertainty surrounding the risk and likelihood of developing a radiation-induced malignancy from CT scan. However, at our current level of understanding, it appears unwise to assume that there is no increased risk and, thereby, to expose patients to doses that future study may reveal to be critical.26 Chest physicians can minimize
Acknowledgments
Financial/nonfinancial disclosures: The authors have reported to CHEST that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.
Other contributions: Jana Johnson provided additional editorial and formatting assistance. We thank Julie Felice, CPM, and Ulrich Rassner, MD, for their advice on the topic of medical physics.
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