Radiation Exposure

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; risks must be 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

RADIATION TERMINOLOGY

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• In the Système International (SI) nomenclature, the rad has been replaced by the gray (Gy), and 1 rad equals 0.01 Gy = 1 cGy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

Symptoms and Signs

SKIN AND MUCOUS MEMBRANES

• Erythema

• Epilation

• Fingernail destruction

• Epidermolysis

HEMATOPOIETIC TISSUES

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

CARDIOVASCULAR SYSTEM

• 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

UROGENITAL SYSTEM

• 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

PULMONARY SYSTEM

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

GASTROINTESTINAL SYSTEM

• Mucositis and mucosal edema may occur within hours or days after exposure

• Odynophagia

• Anorexia

• Nausea, vomiting

• Dehydration

• Weakness

• Inflammation and ulceration of the bowels caused by high doses of radiation

• The stomach and colon are the gastrointestinal organs most at risk for cancer induction due to internal radiation

ENDOCRINE SYSTEM

• Thyroid dysfunction (hypothyroidism) may be delayed effect of high-dose (eg, therapeutic) radiation

• Relatively resistant to low or moderate doses of radiation

  • Normal thyroid

  • Pituitary

  • Pancreas

  • Adrenals

  • Bladder

  • Parathyroid glands (especially resistant)

NERVOUS SYSTEM

• Brain and spinal cord are more sensitive to acute exposures than peripheral nerves

SYSTEMIC REACTION (ACUTE RADIATION SYNDROME)

• Anorexia, nausea, vomiting, weakness, exhaustion, lassitude, and prostration may occur, singly or in combination

• Dehydration, anemia, and infection may follow

Laboratory Tests

• Serial lymphocyte counts are useful for dose estimation and monitoring of the clinical impact of exposure

Medications

• Hematopoietic growth factors (ie, G-CSF and GM-CSF) have been effective in accelerating hematopoietic recovery after bone marrow suppression from ionizing radiation

• Useful supportive measures include

  • Antiemetics

  • Fluid and electrolyte support

  • Blood and platelet transfusions

  • Blood stem cell transplantation

  • Bone marrow transplants

  • Prophylaxis against malignancy

  • Antimicrobials

Therapeutic Procedures

ACCIDENTAL RADIATION EXPOSURE

• Particulate or radioisotope exposures must be decontaminated in designated confined areas

• For many radioisotopes, chelation, blocking, or dilution therapy is indicated

• Treatment of systemic reactions is symptomatic and supportive

THERAPEUTIC RADIATION EXPOSURE

• Radiation therapy is a successful component to treating many malignancies

• Cancer survivors treated with radiation therapy are an important resource to review and quantify associations between radiation therapy and risk of long-term adverse health and quality of life outcomes

• These patients have a higher risk of development of a second malignancy; obesity; and pulmonary, cardiac and thyroid dysfunction, as well as an increased overall risk for chronic health conditions and mortality

Complications

• Skin scarring, atrophy, telangiectasis, and xerostomia

• Cataract, dry eye syndrome, retinopathy

• Anemia, thrombocytopenia, bone marrow suppression

• Neuropathy, myelopathy, cerebral injury

• Obliterative endarteritis, coronary artery disease, pericarditis with effusion, constrictive pericarditis

• Thyroid disease

• Pulmonary fibrosis

• Hepatitis, liver dysfunction

• Intestinal stenosis

• Nephritis, kidney dysfunction

• Neoplastic disease (eg, leukemia and cancers of the skin, breast, lung, and thyroid) is increased after exposure to radiation at relatively low doses (< 0.2 Gy)

• High-dose radon exposure is associated with an increased risk of lung cancer

• Microcephaly and other congenital abnormalities may occur in children exposed to radiation in utero, especially early in pregnancy

Prognosis

• X-rays and CTs are classified as carcinogens since exposure causes leukemia, and cancers of the thyroid, breast and lung

• Death after acute lethal radiation exposure is due to

  • Hematopoietic failure (ie, hemorrhage, anemia, leucopenia, and immunosuppression)

  • Gastrointestinal mucosal damage

  • CNS damage

  • Widespread vascular injury

  • Secondary infection

• Carcinogenesis is related to the total dose, duration, accumulation of exposure and to the susceptibility of the victim

• Radiation-related cancer risks persist throughout the exposed person's lifespan

• Nuclear radiation exposure increases cancer risk (eg, among those exposed at Chernobyl, Hiroshima, Nagasaki and Marshall Island nuclear test detonations)

When to Admit

• Most patients with significant ionizing radiation exposure require admission for close monitoring and supportive treatment