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.
Water: 80% - A simple molecule.
Protein: 15% - A macromolecule.
Fat: 2% - A macromolecule.
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. Chromosomes: Damage to lymphocytes can produce both an early and a late response. Cataracts: The eye's sensitivity is age dependent. Increase in age, increases effects. Cataracts at 1,000 Rad Life Span Shortening
10 days per rad: You can loose 10 days of life for every rad received. Relative safety of occupation: Radiologic Technology is considered a safe occupation. Risk Estimates
Relative Risk: Observed cases ÷ Expected cases. Estimate used when you don't know the original dose. Excess Risk: Observed cases - Expected cases. Estimate using the excess cases induced. Absolute Risk: Estimate using 2 known dose levels.
Radiation Induced Malignancy
Leukemia: Linear, Non-threshold. 4-7 year latent period. 20 year "at risk" period. Thyroid Cancer: Linear, Non-threshold dose/response relationship. Bone Cancer: Radium watch-dial painters developed bone cancer. Skin Cancer: Follows a threshold dose/response relationship. Breast Cancer: Atomic blast survivors who received 10 Rads plus, exhibited a risk factor of 4:1. Lung Cancer: Uranium miners show a risk factor of 8:1.
Liver Cancer: "Thorotrast" contrast agent, caused liver cancer after 15-20 year latent period. Total Risk of Malignancy
Overall Absolute Risk of Malignancy: (p.487)...