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Radiation Biology. Cellular Level Cell Sensitivity Radiolysis of Water Direct Effect/Indirect Effect Target Theory Radiation Effect Early Effects Prodromal/Latent period/Manifest Illness Hematopoietic Syndrome GI Syndrome CNS Syndrome Local tissue damage Late Effects

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Radiation Biology

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Radiation Biology

Cellular Level

Cell Sensitivity

Radiolysis of Water

Direct Effect/Indirect Effect

Target Theory

Radiation Effect

Early Effects

Prodromal/Latent period/Manifest Illness

Hematopoietic Syndrome

GI Syndrome

CNS Syndrome

Local tissue damage

Late Effects

Local Tissue Effect

Life Span shortening

Radiation Protection

Time Distance Shielding

Shield Types


Radiation Biology

Largest sources of man-made radiation are medical and dental x-rays.


Radiation Biology

Cellular Level

Cellular Levels

Cell Sensitivity

  • Early Effect:

  • radiation response occurs within minutes/days after exposure

  • acute radiation syndrome

  • local tissue damage

  • Late Effect:

  • radiation response not observable for months or years

  • leukemia

    • cataracts

  • other cancers

  • local tissue damage

  • Life span shortening

  • genetic damage

  • Cell Sensitivity

    Cell Sensitivity

    • Linear Response to radiation:

    • Non-threshold

      • Assumes no dose is safe

    • Threshold assumes

      • Minimum dose needed to produce a response



    A dose response relationship is produced by extrapolating high dose experimental

    data to low doses.

    Diagnostic radiology is almost exclusively concerned with the late of effects for radiation exposure. This assumes a linear non-threshold dose-response relationship. However, no dose is considered safe.

    Cell Sensitivity

    Basic Cell Structure

    • Two parts:

      • Nucleus- contains DNA

      • Cytoplasm is 80% water

    • DNA is at risk when a cell is exposed to ionizing radiation

    Two Basic Cell types

    Cell Structure

    Radiolysis of Water

    Ionization radiation interacts with a water (H2O). Water dissociates into

    2 ions. This process creates free radicals. These are uncharged molecules

    containing as single unpaired electron in outer shell.

    • H 2 O molecules -

    • Ejection of electron = free radical

    • H2 0 2 = hydrogen peroxide

    Radiolysis of Water

    HOH+ recombine to H2O

    Direct/Indirect Effect

    Let’s Play Jenga !!

    Target Theory

    Target theory suggests that a key molecule must be

    inactivated. The key molecule is assumed to be DNA.

    • When interaction occurs between radiation and target molecule, it is

    • considered a “hit”

    • An indirect hit has a larger target area because of the mobility

    • of the free radicals

    • Radiation acts randomly.

    B3…..miss……..A4…..hit…….You sunk my Battleship!!!

    Radiation Effects

    • Three different levels of exposure effects:

    • Hematologic syndrome

    • GI syndrome

    • CNS syndrome

    Acute Radiation Syndrome – full body exposure given in a few minutes.


    Each syndrome has 3 main sub-stages

    prodromal stage

    latent stage

    manifest illness

    cell death/repair

    Early Effects

    • Acute Radiation Syndromes – full body exposure given in a few minutes.

    • 3 stages of response:

      1. Prodromal -NVD stage (nausea, vomiting, diarrhea)

      2. Latent Period-Feels well while undergoing biological changes

      3. Manifest Illness-Full effects felt, leads to recovery or death

    Total Body Response to Radiation

    • Hematologic : results in infection, hemorrhage & anemia

    • Gastrointestinal : results in diarrhea, nausea & vomiting, fever

    • Central Nervous System : results in convulsions, coma, & eventual death from increased intracranial pressure.

      CNS least sensitive in ADULTS –

      MOST sensitive in the FETUS

    3 Radiation Syndromes

    Cherynobyl Fall out

    For Chernobyl:

    • 11,000 mrem- current background in red zones

    • 12 mrem is your average background radiation.

    • This is a thousand times greater than the normal background level of radiation

    • Approximately 15-20% of babies are born healthy.

    Exposure in soil & water

    • Late Effects

      • Local Tissue Effect

        • Erythema

        • Cataracts

      • Life Span Shortening

      • Cancers/Malignancies

      • Genetic Effects

    Late Effects

    • Somatic Effects: develop in the individual who is exposed

      • Most common:

        • Skin Damage, Cataract formation & Carcinogenesis

    • Genetic Effects: develop in future generations as a result of damage to germ cells.

    Late Effects of Radiation

    Fukushima 50 occupational exposure due to rescue work

    After reading this article, write your thoughts on the rescue workers in Japan.

    Include allowable exposures to workers, possible acute affects, their prognosis

    for long term health.

    Fukushima, Japan

    • Cardinal Principles of Radiation Protection




    • ALARA

    Radiation Protection

    Cardinal Principles of Radiation Protection

    Time Distance and Shielding

    • Triad of Radiation Safety

      1. Time

      2. Distance

      3. Shielding

      *Apply to the patient & Technologist

    Cardinal Principles of Protection



    Skin burns from 30 min of beam on time

    Over Radiation to SkinToo much time under beam

    Acute Localized Radiation Effects

    The Table 2-2 provides examples of possible radiation effects to skin caused by typical fluoroscopy exposures. Note that patient and technique factors can substantially increase exposure rates, significantly reducing the time necessary for the subsequent effect.

    Table 2-2: Dose and Time to Initiate Localized Radiation Effects

    .7 of an hour is approximately 42 miutes


    This is an actual arm tatoo. Now that’s dedication !

    Inverse square law

    Inverse square law

    Inverse square law



    A lead protective shield is placed

    • Between the x-ray tube and the individuals exposed

    • Absorbs unnecessary radiation

    • Contact

    • Shaped

    • Shadow



    Shadow Shields

    Breast ShieldShadow shields

    1. TECHNOLOGIST . 25 mm LEAD

    • Lead apron

    • Gloves

    • Thyroid shield

    • Glasses

      2. PATIENT – . 5 mm LEAD

    • Gondal Shielding



    As Low As Reasonably Achievable

    Primary Barriers

    Stay out of primary beam

    Image Wisely website

    Image Wisely





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