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For further information, see CMDT Part 37-12: Radiation Exposure

Key Features

Essentials of Diagnosis

  • Damage from radiation is determined by the source, type, quantity, duration, bodily location and susceptibility and accumulation of exposures of the person

  • Radiation exposure from medical diagnostic imaging

    • Has risen dramatically over the past few decades

    • Needs standardization and regulation of radiation dosing

  • Clinicians and patients must be educated regarding the risks of medical diagnostic radiation weighed against the benefits of the medical imaging needed

  • All patients should keep records of their medical imaging radiation exposures, and copies of the medical images and interpretations

General Considerations

  • Nonionizing radiation

    • Low energy

    • Results in injuries related to local thermal damage (ie, microwave and radiowave)

  • Ionizing radiation

    • High energy

    • Causes cellular disruption, DNA damage, and mutations

    • Categorized as either electromagnetic (ie, x-rays and gamma rays) or particulate, (ie, alpha or beta particles, neutrons, and protons)

    • Exposure may be external, internal or both

  • Exposure to radiation may occur from environmental, occupational, medical care, accidental, or intentional (ie, terrorism) sources


  • Roentgen (R) refers to the amount of radiation dose delivered to the body

  • A rad is the unit of absorbed dose

  • A rem is the unit of any radiation dose to body tissue in terms of its estimated biological effect

  • For x-ray or gamma-ray radiation, roentgens, rems and rads are virtually the same

  • For particulate radiation from radioactive materials, these terms may differ greatly (eg, for neutrons, 1 rad equals 10 rems)

  • In the Système International (SI) nomenclature, the rad has been replaced by the gray (Gy), and 1 rad equals 0.01 Gy = 1 cGy

  • The SI replacement for the rem is the Sievert (Sv), and 1 rem equals 0.01 Sv

Clinical Findings

Symptoms and Signs


  • Erythema

  • Epilation

  • Fingernail destruction

  • Epidermolysis


  • Injury to bone marrow may vary from transient decreases to complete destruction of blood elements


  • Pericarditis with effusion or constrictive pericarditis after months or years

  • Myocarditis less common

  • Smaller vessels (the capillaries and arterioles) more readily damaged than larger ones


  • Males

    • Small single dose (200–300 cGy) cause temporary aspermatogenesis

    • Larger doses (600–800 cGy) cause permanent sterility

  • Females

    • Single dose of 200 cGy may cause temporary cessation of menses

    • 500–800 cGy causes permanent castration

  • Moderate–heavy irradiation of embryo in utero results in injury to fetus or embryonic death/spontaneous abortion


  • High or repeated moderate doses may cause pneumonitis or pulmonary fibrosis, often delayed for weeks or months


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