Biologic Effects of Ionizing Radiation

• Leukopenia is when a patient has low white blood cell count, is a somatic, early tissue reaction with a threshold, and is non-stochastic and deterministic
• Cancer is a somatic, late somatic, and stochastic reaction that has no threshold and is not deterministic
• Genetic mutation is a genetic, stochastic, and non-deterministic reaction with no threshold that occurs later
• Cataracts are a somatic and late tissue reaction

Biologic Effects of Ionizing Radiation

• Biologic effects fall into 2 categories: Somatic and Genetic
• Somatic effects happen to the body that was irradiated
• Genetic effects happen to future generations
• Early somatic effects happen within minutes or weeks
• Late somatic effects happen within months or years
• All tissue reactions, early and late, have a threshold
• Late stochastic somatic effects have no threshold

Somatic Effects

• This is biologic damage sustained by living organisms as a consequence of exposure to ionizing radiation
• Depending on the length of time from irradiation to the first symptoms, the effects are classified as early or late

Early Tissue Reactions

• May appear within minutes, hours, days, or weeks and require a substantial dose of radiation
• Severity of the effects increases as the radiation dose increases
• Diagnostic imaging exams typically do not impose enough radiation to cause early tissue reactions
• Skin effects primarily come from unacceptably high x-ray exposures in radiology
• Prolonged exposure to x-rays can result in a high radiation dose to the skin

Possible High Radiation Dose Consequences

• These include nausea, fatigue, and erythema
• Also includes epilation, which is loss of hair
• Blood and intestinal disorders
• Fever, dry or moist desquamation, depressed sperm count
• Temporary or permanent sterility
• Injury to the central nervous system

Acute Radiation Syndrome (ARS)

• Whole-body dose of 6 Gyt can result in many manifestations
• ARS is radiation sickness
• It occurs after whole-body reception of large doses of ionizing radiation delivered over a short period of time
• Epidemiologic data from atomic bomb survivors and nuclear accident victims have provided key insights
• ARS is a syndrome, a collection of symptoms from high-level radiation exposure

ARS Stages

• There are 4 main stages to ARS:
• Prodromal is the initial, mild stage
• Latent is where there are no symptoms, is hidden/invisible
• Manifest is the stage where there 3 subsyndromes
• Hematopoietic, Gastrointestinal and Cerebrovascular
• Death or recovery is the last stage
• The sub-syndromes of the manifest stage are dose-related, and related to blood/contrition damage, bone marrow damage, plus nervous system damage

Manifest Stage Subsyndromes

• Hematopoietic syndrome occurs with 1-10 Gyt and can be treated to sustain life up to 6-8 weeks
• Gastrointestinal syndrome occurs with 6-10 Gyt and can be treated to sustain life up to 3-10 days
• Cerebrovascular syndrome occurs with 50 Gyt + and can be treated to sustain life up to a few hours or days

Causes of Death in Each Subsyndrome

• Hematologic death is from excessive bone marrow destruction that causes anemia
• Gastrointestinal results from catastrophic damage to the epithelial cells that line the GI tract
• Cerebrovascular death is from the failure of the central nervous system/cardiovascular systems

ARS/Chernobyl

• Massive explosion at the Chernobyl Nuclear plant on April 26, 1986
• A case where humans developed ARS
• 2 of 444 workers died instantly, and 29 died within 3 months because of thermal trauma
• They got doses of ionizing radiation of approximately 6 Gyt or more and it caused at least 203 other people to be hospitalized
• The occurrence of nausea and excessive vomiting played an essential role in identification of radiation casualties within the first 2 days

ARS/Atomic Bombing

• The Japanese atomic bomb survivors are examples of a human population affected by ARS
• Follow-up studies of survivors who did not die of ARS demonstrated late tissue reactions and stochastic effects of ionizing radiation
• Created an awareness of the need for a thorough understanding of ARS and appropriate medical support of persons affected

Lethal Dose

• LD 50/30 is the whole-body dose of radiation that can be lethal to 50% of the exposed population within 30 days
• For adult humans the estimated dose is 3-4 Gyt.
• Whole-body doses greater than 8 Gyt will cause the death of the entire population in 30 days without medical support
• LD 50/60 for humans is perhaps the most accurate measure for human survival, the number indicates time length
• If medical treatment is provided promptly, the patient is treated for initial symptoms, and so long-term survival may be delayed