1. Indirect Effect
    • previously mentioned
    • agents produce indirect effects because the damage is not caused by the
    • radiation but the indirect effect of the radiation.
  2. Effects on DNA
    •Single strand break

    • –Point mutation, commonly occur
    • with low LET

    indirect bc low LET

    •Easy type of damage to repair
  3. Target Theory
    • •Basically, the DNA molecule is the most
    • important molecule

    • •Therefore, if the DNA molecule is hit and
    • inactivated the cell will most likely die

    water 80% DNA 1%
  4. Cellular Effects of
    •Instant death

    –1000 Gy in a few seconds

    • •Reproductive death at the cellular level
    • –10 Gy

    • •Apoptosis
    • –Cells die without attempting cell
    • division
  5. Cellular Effects of
    •Loss of function

    • •Chromosome breakage
    • –Can lead to genetic effects
    • changes are passed down
  6. Mitotic death
    • Cell death occurs after cell
    • division
  7. Mitotic delay
    • Mitosis occurs after missing a
    • division cycle
  8. Cell sensitivity
    Immature cells

    • –Non-specialized and rapid cell
    • division

    • –Both conditions that encourage
    • radio-sensitivity
  9. Cells are radio sensitive in?
  10. immature cells more radiosensitivity than?
  11. Lethal Dose

    –300 – 400 rads, 3 – 4 grays

    • •Expressed as LD50/30
    • in most mammals or LD50/60 in humans

    • blood cell count problem;GI tract problem
    • –The first number is percentage of
    • effect (death) second number is how many days for the effect to occur
  12. Dose-Response Curves
    • •Linear or non-linear
    • •Threshold or non-threshold

    • Type of curve depends on the effect being
    • observed or reported
  13. Radiation Protection
    •Based on a linear non-threshold curve

    •Any radiation has the potential for problems

    •This is the most cautious curve.
  14. Early non-stochastic
    • •Occur within weeks of exposure
    • –Nausea
    • –Fatigue = no blood cell
    • –Erythema
    • –Epilation =hair loss
    • –Symptoms of these effects

    • •Generally, classified as Acute Radiation
    • Syndromes
  15. ARS

    • –Prodromal
    • Symptoms will be present

    • –Latent
    • Symptoms will resolve or be
    • dormant

    • –Manifest
    • You got problems
  16. ARS
    Acute radiation syndrome
  17. Types of ARS
    • Hematopoietic
    • 100 – 1000 rads

    • GI
    • 600 – 1000 rads

    • Cerebrovascular
    • Up to 5000 rads

    •Death in 2 to 3 days
  18. Late Non-stochastic


    • •Organ atrophy
    • Loss of parenchymal cells

    • •Decreased fertility
    • sterility
  19. Late Stochastic Effects

    •Genetic defects
  20. Embryologic Effects
    • •Most sensitive during organogenesis
    • 10 days to 6 weeks
    • 2 weeks to 8 weeks
  21. Effective Dose Limiting
    • The idea that exposure to radiation can/may
    • induce cancer.

    • The result is that radiation
    • protection guidelines are based on the possibility of getting cancer not some
    • other effect.

    minimize cancer
  22. Radiation Safety Program
    • •All facilities must have a radiation
    • protection/safety program in place.

    •Radiation Safety Committee

    –Radiation safety Officer (RSO)
  23. Effective Dose Limiting
    • •Looks to establish the upper limit of
    • exposure to ionizing radiation resulting in a negligible risk of injury or
    • genetic defect.

    • •Can be whole body, partial body (extremity,
    • eye) and individual organs.

    • –Non-stochastic (deterministic)
    • and stochastic (probabilistic)

    • •Occupational limits are based on comparing
    • outcomes against other occupational hazards.
  24. Radiation Induced
    Responses - non-stochastic
    •Non-stochastic = Somatic


    –Directly related to the dose received, threshold



    –Decreased blood count


    –Acute Radiation Syndromes (ARS)





    –Organ atrophy
  25. Radiation Induced
    Responses - Stochastic
    Stochastic = Genetic


    • –Mutational, non-threshold,
    • randomly occurring, all or nothing

    • –The greater the dose the greater
    • the chance of the effect occurring.  NOT
    • is it going to occur.

    –Cancer and genetic effects
  26. Basis for Effective Dose
    Limiting System
    • While we have already discussed the fact
    • different forms have radiation have different effects (equivalent dose) some
    • tissues are more sensitive than others.

    • •Tissue weighting factor allows overall risk
    • to be determined.
  27. Occupational MPD
    •50 mSv or 5 rem annually


    –0.5 mSv per month

    • –5 mSv for
    • the entire pregnancy
  28. Radiation Hormesis
    • •The potential that small radiation exposure
    • is actually beneficial.
  29. Public MPD
    •1 mSv or 0.1 rem or 100 mrem year

    •Educational exposure

    • –1 mSv or
    • 0.1 rem annually

    • –Notice it is the same as the
    • general public
  30. RBE
    Relative biologic effectiveness
  31. OER
    Oxygen enhancement ratio
  32. Low energy LET
    X-rays and gamma rays

    Penetrating and randomly interactive

    Most damage is thru indirect effect and is sublethal; therefore repairable dmg
  33. High energy LET
    Particulate radiation is the most common from of this

    Typically have both mass and electrical charge

    More destructive than low LET radiation
  34. Low LET with DNA
    Low probability of interacting with DNA

    • Most damage is indirect
    • Dmg can usually be repaired
  35. Hight LET with DNA
    Higher probability of interacting with DNA and damaging it

    Non repairable
  36. Relative biologic effectiveness
    • Specific cells and tissues
    • Diagnostic radiography weighting factor are used

    Effective dose, what cells get irradiated
  37. OER with high LET radiation
    OER is less with high LET radiation

    Most damage is direct
  38. OER with Low LET X-rays
    OER is higher with low LET X-rays
  39. Oxygen is producing peroxides = ?
  40. Direct effect
    The incoming photon strikes the DNA molecule directly causing ionization of the DNA
  41. Radiolysis of water
    Photon strikes water molecule and create ion pair

    • Hydrogen ion
    • Hydroxyl ion
    • Both solvents
  42. Hydrogen radical =
    Additional Dmg

    Corrosive human tissue
  43. Free radicals
    Contain an unpaired outer shell electron and are unstable and reactive

    They can also travel an transfer energy damaging other cells
  44. Combining free radicals in to caustic agents -
    • Hydrogen peroxide
    • Hydroperoxly radical
  45. Free radicals are
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