Elsevier

Mayo Clinic Proceedings

Volume 85, Issue 12, December 2010, Pages 1142-1146
Mayo Clinic Proceedings

CONCISE REVIEW FOR CLINICIANS
Radiation Risk From Medical Imaging

https://doi.org/10.4065/mcp.2010.0260Get rights and content

This review provides a practical overview of the excess cancer risks related to radiation from medical imaging. Primary care physicians should have a basic understanding of these risks. Because of recent attention to this issue, patients are more likely to express concerns over radiation risk. In addition, physicians can play a role in reducing radiation risk to their patients by considering these risks when making imaging referrals. This review provides a brief overview of the evidence pertaining to low-level radiation and excess cancer risks and addresses the radiation doses and risks from common medical imaging studies. Specific subsets of patients may be at greater risk from radiation exposure, and radiation risk should be considered carefully in these patients. Recent technical innovations have contributed to lowering the radiation dose from computed tomography, and the referring physician should be aware of these innovations in making imaging referrals.

Section snippets

Radiation Dose

Absorbed dose, measured in grays (Gy), quantifies the energy deposited per unit mass. The energy deposition of 1 J/kg of tissue is the equivalent of 1 Gy. Because not all types of radiation produce the same biological effect, the dose equivalent is often used instead of the absorbed dose. The dose equivalent is the product of the absorbed dose and a radiation weighting factor and is expressed in sieverts (Sv). Because the radiation weighting factor for x-rays and gamma rays is 1.0, 1 Gy is

Excess Cancer Risk From Radiation: The Evidence

The relevant biological effect of x-rays and gamma rays is secondary to ionization. Ionization of water molecules can create hydroxyl radicals that may interact with DNA to cause strand breaks or base damage; DNA can also be ionized directly. Although most radiation-induced damage is rapidly repaired, misrepair can lead to point mutations, chromosome translocations, and gene fusions that are linked to cancer induction.1 This effect is typically thought to be stochastic, ie, it can occur at any

Radiation Dose From Imaging Examinations

A useful way to understand radiation doses from diagnostic examinations is to compare them to average natural background radiation (3 mSv per year) (Table).2, 6, 17

Radiation doses are sometimes expressed as entrance skin doses. Entrance skin doses are used in conventional radiography: a dose estimate at 1 point in the beam allows estimates of organ doses and effective dose. To assess the health risks of low doses of ionizing radiation, the International Commission on Radiation Protection uses

Reducing Patient Radiation Dose

Radiation dose from an imaging study can be reduced by 3 methods. First, one can decide not to perform the study at all. Such a decision should be based on proper understanding of the indications of the study, review of any previous imaging that might have already reasonably answered a clinical question, and an assessment of any special patient considerations that increase or decrease risk. Second, an alternative study that does not use ionizing radiation can be selected. Third, less radiation

CONCLUSION

A basic knowledge of radiation risk is useful in counseling patients who express concern about this issue. In most cases, the benefits of indicated medical imaging will outweigh the relatively small excess cancer risk, and patient management should not be altered on the basis of radiation risk. However, for certain subsets of patients, radiation risk should be of greater concern to the clinician. In addition, clinicians can play a role in minimizing radiation risk to their patients by referring

CME Questions About Radiation Risk

  • 1.

    Which one of the following is the average annual background radiation dose?

    • a.

      0.001 mSv

    • b.

      0.7 mSv

    • c.

      3 mSv

    • d.

      10 mSv

    • e.

      50 mSv

  • 2.

    Which one of the following is an average effective radiation dose from single-phase computed tomography (CT) of the abdomen and pelvis?

    • a.

      0.001 mSv

    • b.

      0.7 mSv

    • c.

      3 mSv

    • d.

      10 mSv

    • e.

      50 mSv

  • 3.

    Which one of the following is the average effective radiation dose from screening mammography (2 views)?

    • a.

      0.001 mSv

    • b.

      0.7 mSv

    • c.

      3 mSv

    • d.

      10 mSv

    • e.

      50 mSv

  • 4.

    Which one of the following statements is false?

    • a.

      The

REFERENCES (29)

  • FR Verdun et al.

    Radiation risk: what you should know to tell your patient

    Radiographics

    (2008)
  • Radiation exposure from x-ray examinations. RadiologyInfo.org Web site....
  • MP Little et al.

    Risks associated with low doses and low dose rates of ionizing radiation: why linearity may be (almost) the best we can do

    Radiology

    (2009)
  • DA Pierce et al.

    Radiation-induced cancer risks at low doses among atomic bomb survivors

    Radiat Res

    (2000)
  • Cited by (376)

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    On completion of this article, you should be able to (1) recognize the doses of common medical imaging studies, (2) recognize which patients may be at increased risk from radiation, and (3) be familiar with the evidentiary base for determining excess cancer risks from low-dose radiation.

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