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

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

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.

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

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

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

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

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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