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WEEK 8RADIATION BIOLOGY
Fall 2012
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THE EARLY YEARS
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Biological Response toIonizing Radiation
1. Can cause biological changes
2. Technologists should have an understanding of:
1. Cellular biology 2. How radiation interacts with cells in order to
protect oneself and the patient.
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Early Effects of Radiaton
• 1 Erythema• 2 Blood changes• 3 Epilations (hair loss)• 4Acute Radiation Syndrome• 5 Ulcers
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Late Effects of Radiaton
• 1 Cataracts• 2 cancer• 3 Organ atrophy• 4 Reduced Fertility• 5 Sterility
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8FIG. 9–7 Graph indicates no-threshold versus threshold response to radiation.
Elsevier items and derived items © 2007, 2003 by Saunders, an imprint of Elsevier Inc.
Linear Response to radiation:
1. Assumes no dose is safe
2. Diagnostic radiation:
• Non threshold
3. Low dose over long period of time
4. Early Radiology Exposure
5. Threshold
• Amount needed to see affect
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EFFECTS OF RADIATION
1. Late effects:A. Somatic effects
• Individual exposed
B. Genetic effects• Future generations
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Somatic Cells
1. Perform all the body’s functions.
2. Possess 2 of every gene on two different chromosomes.
3. Divide through the process of mitosis
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Germ Cells
1. Reproductive cells of an organism.
2. Half the number of chromosomes as the somatic cells.
3. Reproduce through the process of meiosis.
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SOMATIC & GENETICSTOCHASTIC VS NON STOCHASTIC
A) _Chanced_EFFECTS1. Genetic damage2. Leukemia3. Cancer4. Diagnostic radiology
BB)_Determined__Dose1. Skin erythema2. Catracts3. Sterility4. Malignancies
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Cell Structure
1. Biologic response to ionizing radiation depends on cell structure
2. Comprised of:– Nucleus– Cytoplasm– Chromosomes (made up of genes)
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Basic Cell Structure
1. Two parts:1. Nucleus- contains
DNA2. Cytoplasm is 80%
water
2. DNA is at risk when a cell is exposed to ionizing radiation
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Cell Type Examples
1. Radiosensitive: 1. Skin cells2. Small intestine cells,3. Germ cells
2. Radioresistant_: 1. Specialized in structure and function, 2. Do not undergo repeated mitosis
1. Nerve, muscle & brain cells
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Radiosensitivity of Cells
1. Bergonie & Tribondeau (1906) – method of classifying a cell’s response to radiation according to sensitivity.
2. Cells are most sensitive during active division (primitive in structure & function).
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The Law of Bergonie & Tribondeau
Cells that are most sensitive to radiation are:
• Young – immature cells• Stem Cells• Highly dividing (mitotic) cells
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RADIOSENSITIVITY OF CELLS
1. Mitotic activity 2. Specific characterisitics of
the cell (primative)– Structure– Function
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Cellular Response to Radiation
1. Die before mitosis
2. Delayed mitosis
3. Failure to divide at normal mitotic rate
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Example of cell sensitivity
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Direct Hit and Indirect Hit
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Cellular AbsorptionDirect vs. Indirect Hit
Direct Hit Theory:1. When radiation
interacts with DNA
2. Break in the bases or phosphate bonds
3. Can injure or kill the cell
Indirect Hit Theory:1. Occurs when water
molecules are ionized
2. Produces chemical changes – 1. Can injure or kill cell
3. Vast majority of cellular damage is from indirect hit
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TARGET THEORY1. Photons hit master
molecule DNA
1. cell dies
2. Doesn’t hit nucleus –
1. Passes through
2. No essential damage
3. Hormoresis
1. repair that can occur when below 5 rads of expsoure
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Cell bombarded with photonsWhat damage will they cause?
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Radiolysispoison water theory
1. H 2 O molecules -2. Ejection of electron = free
radical 3. H2 0 2 = hydrogen peroxide
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HOH+ recombine to H2O
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Radiation Exposure and Cancer
What are some of the causes of cancer?
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Acute Radiation Syndrome
Full body exposure given within minutes
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Total Body Response to Radiaiton
• Acute Radiation Syndrome – full body exposure given in a few minutes.
• 3 stages of response:1. Prodromal Stage: NVD stage
(nausea, vomiting, diarrhea)2. Latent Period: Feels well while undergoing biological changes3. Manifest Stage: Full effects felt, leads to recovery or death
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3 Radiation Syndromes 1. Bone marrow syndrome: results in infection,
hemorrhage & anemia (200-1000 rad)1. 6-8 weeks
2. Gastrointestinal syndrome: results in diarrhea, nausea & vomiting, fever ( 1000-5000 rad)
1. 3-10 days
3. Central nervous syndrome: results in convulsions, coma, & eventual death from increased intracranial pressure. (5000 rad or greater)
1. Few hours – 3 days
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Late Effects of Radiation
1. Somatic Effects: develop in the individual who is exposed
– Most common: • Cataract formation & Carcinogenesis
2. Genetic Effects: develop in future generations as a result of damage to germ cells.
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Instances of Acute Radiation Exposure
1) Nagasaki and Hiroshima2) Chernobyl
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Hiroshima Nagasaki
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Cherynobyl - immediately
• Shortly after the blast– 20 R in less than 1 minute – clean up crew– fireman – 600,000 “liquidators” exposed
• A pilot saw a village where the dosimeter, the reading had gone off the scale– 500 roentgen per hour: – 'Above 500, the equipment - and human beings - aren't supposed to
work.– he had flown in 1,500 roentgen an hour of expoure
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Exposure in soil & water
1. 11,000 mrem- current background in red zones
2. 12 mrem is your average background radiation.
3. This is a thousand times greater than the normal background level of radiation
4. Approximately 15-20% of babies are born healthy.
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Cherynobyl Fall out
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US Nuclear Tests 1945 – 1992
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Nevada Testing Sites
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