RADBIO Midterm Exam

• The only academic interest in diagnostic radiology. Diagnostic x-ray beams are neither intense enough nor large enough to cause death.
• Deterministic Effect


  • Radiation response in humans within few days to months, produced by high radiation doses, biologic response whose severity varies with radiation dose, exhibit increasing severity with increasing radiation dose, dose-response relationship is nonlinear and has a threshold
• Principal Deterministic Effects of Radiation Exposure on Humans and the Approximate Threshold Dose

  • Death (Whole Body, 2 Gy)
  • Hematologic depression (Whole Body, 250 mGy)
  • Skin erythema (Small Field, 2 Gy)
  • Epilation (Small Field, 3 Gy)
  • Chromosome aberration (Whole Body, 50 mGy)
  • Gonadal dysfunction (Local Tissue, 100 mGy)

  
• Acute Radiation Syndrome


  Sequence of events that follow high-level radiation exposure leading to death within days or weeks
• Three Separate Syndromes of Acute Radiation Syndrome

  • Hematologic Death
  • GI Death
  • CNS Death
• Prodromal Period


  Immediate response to radiation sickness
• Latent Period


  Time of exposure during which there is no sign of radiation sickness
• Manifest Illness


  Characteristics or signs and symptoms of an illness
• LD50/60


  Dose of radiation to the whole body that causes 50% of irradiated subjects to die within 60 days

  
• Mean Survival Time


  As the whole-body radiation dose increases, the average time between exposure and death decreases

  
• Local Tissue Damage


  • Every organ and tissue of the body can be affected by partial-body irradiation, effect is cell death which results in shrinkage of the organ or tissue, can lead to total lack of function or recovery
• Deterministic Response


  Minimum dose necessary to produce an effect
• Normal Skin Consists of Three Layers

  • Outer layer (epidermis)
  • Intermediate layer of connective tissue (dermis)
  • Subcutaneous layer of fat and connective tissue

  
• Basal Cells


  Lowest layer of epidermis, stem cells that migrate to the surface and are slowly lost and replaced
• Erythema


  Sunburn-like reddening of the skin, first observed biological response to radiation exposure
• Desquamation


  Ulceration and denudation of the skin, first observed biological response to radiation exposure
• Epilation

  Loss of hair, response of the skin to radiation exposure
• Grenz Rays

  Soft x-rays (10-20 kVp) used as treatment for skin diseases
• Human Gonads

  • Critically important target organs, particularly sensitive to radiation, gametogenesis process where germ cells are produced
• Oogonia

  Stem cells of the ovaries
• Oocytes


  Germ cells that develop from oogonia during fetal life and remain in suspended state until puberty
• Spermatogonia


  Male stem cells that mature into spermatozoa over 3-5 weeks
• Irradiation of ovaries early in life


  Reduces ovary size through germ cell death, suppresses and delays menstruation after puberty
• Irradiation of testes


  Causes atrophy similar to ovaries
• Hematologic Effects


  Depressed number of blood cells in peripheral circulation, all blood cells develop from a single pluripotential stem cell

  
• Cell Types Produced from Pluripotential Stem Cell

  • Lymphocytes
  • Granulocytes
  • Thrombocytes
  • Erythrocytes

  
• Lymphopenia


  Reduction in number of lymphocytes, first cell affected after radiation exposure
• Granulocytosis


  Rapid rise in granulocyte count after radiation exposure, followed by granulocytopenia
• Thrombocytopenia


  Depletion of platelets after radiation exposure, develops more slowly than other blood cells
• Cytogenetic Effects


  Study of genetics of cells, particularly cell chromosomes, radiation can induce various chromosome aberrations that follow a non-threshold dose-response relationship

  
• Granulocytosis


  Rapid rise in number, followed by a rapid decrease then a slower decrease (granulocytopenia)
• Abortive rise in granulocyte count

  May occur 15 to 20 days after irradiation if the radiation dose is moderate

  
• Thrombocytopenia


  Depletion of platelets after irradiation develops more slowly, because of the longer time required for the more sensitive precursor cells to reach maturity
• Erythrocytes


  • Less sensitive than the other blood cells, because of their very long lifetime in the peripheral blood
• Cytogenetics


  The study of the genetics of cells, particularly cell chromosomes
• Radiation cytogenetic studies have shown that nearly every type of chromosome aberration can be radiation-induced and that some aberrations may be specific to radiation

  
• Radiation-induced chromosome aberrations follow a non-threshold dose-response relationship

  
• Attempts to measure chromosome aberrations in patients after diagnostic x-ray examination have been largely unsuccessful, however, some studies involving high-dose fluoroscopy have shown radiation-induced chromosome aberrations soon after the examination was performed

  
• High doses of radiation cause chromosome aberrations

  
• Low doses, also do so, but it is technically difficult to observe aberrations at doses that are less than approximately 100 mGy (10rad). An even more difficult task is to identify the link between radiation-induced chromosome aberrations and latent illness or disease