Radiation Protection & Radiobiology Notes
Radiation Protection & Radiobiology Notes Human Biology • Human Response To Ionizing Radiation • Early Effects of Radiation: When response occurs within minutes or days after exposure. • Late Effects of Radiation: When response is not observed for many months or years after exposure. • Effects of fetal irradiation: Death, malformation, malignancy, diminished growth. • Composition of Human Body • Cell Theory: 85% of the body is hydrogen and oxygen. • • Hydrogen: 60% • Oxygen: 25.7% • Carbon: 10.7% • Nitrogen: 2.4% • • Molecular Composition • Water: 80% – A simple molecule. • Protein: 15% – A macromolecule. • Fat: 2% – A macromolecule. • Other: 3% • Tissues and Organs: (The most radiosensitive cells in the human body are Lymphocytes & Spermatogonia. . Fundamental Principles of Radiobiology • Law of Bergonie and Tribondeau • 1) Older cells are more radioresistant. • 2) Younger cells are more radiosensitive. • How these principles apply to radiation safety: The fetus is more radiosensitive to radiation than a child or adult. • Biologic Factors Affecting Radiosensitivity • Age: Humans are most sensitive before birth. • Gender: Females are less radiosensitive than males. . Molecular and Cellular Radiobiology • Irradiation of Macromolecules: (p.450) Follows a Linear, Non-threshold dose/response relationship. • Radiation Effects on DNA: DNA is the most radiosensitive macromolecule. • 1) Cell death • 2) Malignant disease • 3) Genetic damage • Radiolysis of Water: Indirect Effect. Most prevalent in humans. • We are mostly water: 80% Water • The breakdown of water by radiation is harmful. • Breakdown products, called free radicals, cause DNA damage. • DNA damage can cause somatic and genetic outcomes. Direct and Indirect Effect • Direct Effect: Radiation hits DNA causing cell damage. • Indirect Effect: 2 Step process The principle action of radiation on humans is the Indirect Effect. • 1) Radiation breaks down water molecules. • 2) Break down products (free radicals) damage DNA. Single-Target, Single-Hit Model • Poisson Distribution: A statistical law. If 100 rain drops fell on 100 squares, 63% will be wet, 37% will be dry. Early Effects of Radiation • Acute Radiation Lethality: X-ray beams are not large or intense enough to cause radiation lethality. • Early Effects: See a radiation response within a few days. • Local Tissue Damage:Requires a higher dose to produce a response. Results in tissue atrophy. • Skin: Erythema– a sunburn-like redness. SED50 (Skin Erythema Dose to affect 50% of pop.) at 600 Rad. • Gonads: Ovaries & Testes are very sensitive to radiation. Permanent sterility at 500 Rad. Late Effects of Radiation • Local Tissue Effects • Skin: High doses of radiation causes discolored and weathered appearance of skin....
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