Radl 70 Principles of Radiobiology

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swtjo3joe
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Radl 70 Principles of Radiobiology
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2012-03-17 23:05:14
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LET RBE OER target theory indirect action
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principles of radiobiology
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  1. most effects of radiation begin where?
    atomic level
  2. most effects of radiation manifests where?
    cellular level
  3. chemical and biological effects are determined by the degree of what within the tissue?
    ionization
  4. describe low let radiations
    • from x or gamma rays
    • short wavelength, high energy waves
    • sparsely ionizing
    • randomly interact
    • do not give up energy quickly
    • damage is usually indirectly- free radicals are formed
    • may cause single-strand breaks in one side of the DNA ladder
    • usually sublethal- repair enzymes reverse the damage
  5. describe high LET radiation
    • from particles that possess mass and charge
    • alpha particles, particles released from interactions between neutrons and atoms
    • lose energy rapidly than x or gamma
    • produce more ionization per unit length of travel
    • energy is spent sooner than x or gamma
  6. high or low LET radiation is more likely to interact with DNA
    high
  7. what is relative biological effectiveness?
    • the ability of radiation with different LET to produce a biologic reaction
    • x-ray is usually compared to a different source that will produce the same effect
    • expressed as a ratio
    • LET and RBE pertains to radiation
  8. what is oxygen enhancement ratio?
    • pertains to how much oxygen in the tissue
    • the more oxygen there is the more damage can occur
    • more important in rad therapy
  9. what does LET and RBE pertain to?
    radiation
  10. what does OER pertain to?
    the tissue being irradiated
  11. what type of molecules does direct action pertain to?
    • master molecules
    • dna
    • rna
    • enzymes
    • proteins
  12. what type of radiation interactions can occur during a direct action?
    • compton
    • photoelectric
  13. how is direct action harmful?
    • results in breakage of the master molecule's chemical bonds
    • will result in a malfunction of that particular molecule
    • sets off biologic domino effect
  14. what is indirect action?
    interaction of x-ray photons w/ non master molecules mostly water
  15. what is an example of indirect action?
    radiolysis of water- xray hitting a water molecule
  16. radiolysis of water produces what types of ions?
    • a positive water molecule HOH+
    • an electron
  17. how many different reactions can occur after radioloysis of water (HOH+, e-)?
    3
  18. Reaction 1 that can occur after radiolysis of water
    • the positively charge water molecule recombines with an electron
    • a stable water molecule is formed
    • no damage is done
  19. Reaction 2 that can occur after radiolysis of water
    • the electron joins with a water molecule
    • a negative water ion is formed
    • the positive and negative water molecules are unstable
    • these can break apart into smaller molecules
    • free radicals can be formed by this breakup
    • these objects are highly reactive and can do cellular damage
  20. Reaction 3 that can occur after radiolysis of water
    • two of the free radicals can recombine to form hydrogen peroxide
    • highly toxic to cell
    • about two-thirds of all biologic damage is caused by the reaction 2 and 3
  21. what is indirect action?
    the damage caused by the byproduct of radiation (ions) with the macromolecule, not the radiation itself
  22. what is one of the main precursors of indirect action?
    hydrolysis of water
  23. what is point mutation
    • ionizing radiation that rupturesthe chemical bond of a macromolecule severing one of the sugar-phosphate chain siderails of the DNA ladder
    • single strand break
    • repair enzymes can reverse this damage
  24. what may result with point mutation?
    gene mutations
  25. what type of LET radiation can cause point mutation (single strand break)?
    low LET
  26. What type of LET radiation can cause a double strand break?
    high LET
  27. what happens in a double strand break?
    • one or more breaks in each of the two sugar-phosphate chains
    • not repaired as easily as a single strand break
  28. what causes cleaved chromosomes?
    two interactions hit on each side of the sugar phosphate chain
  29. what is a cleaved chromosome?
    • chromosome that is broken in two
    • each new portion contains an unequal amount of genetic material
    • can then divide into defective daughter cells
    • know as mutation
  30. what happens if a chromosome is broke to two or more fragments?
    • can join to another fractured chromosome
    • new formations are known as an aberration
  31. what is restitution?
    • when a broken chromosome rejoins with the broken piece
    • no damage
  32. what is deletion?
    when a part of a chromosome is lost in the next division
  33. what is a broken end rearrangement?
    when a chromosome recombines with another piece of chromosome that appears like a restitution but the genetic material has been rearranged that will alter its function
  34. what is target theory?
    cell death will occur if the master molecule in that cell is inactivated by radiation exposure
  35. which theory is used to explain cell death and nonfatal cell abnormalities caused by radiation exposure?
    target theory
  36. what happens if mutation is genetic?
    • will be seen in future generations
    • this is why we shield gonads
  37. what if mutation is somatic?
    individual consequences only
  38. are radiation effects specific or nonspecific?
    • nonspecific
    • cant tell if an effect came from radiation or someting else
  39. are there certain cancers that are unique to radiation?
    no
  40. how much radiation does it take to cause instant death?
    • 1000 gray of x or gamma ray in a period of seconds or a few minutes
    • 100,000 rads
    • radiation this high do not occur in the diagnostic or therapeutic ranges
  41. how much radiation does it take for reproductive death to occur?
    • 1-10 gray
    • 100-1000 rads
    • cell does not die, but becomes sterile
    • cell will continue to metabolize and synthesize nucleic acids and proteins
    • transmission of damage to future generations is prevented
  42. when a germ cell becomes sterile from radiation exposure, can it transmit its damages to future generations?
    • no
    • it can no longer pass damage to future generations
  43. what is interphase death?
    • interphase is cut short
    • doesnt mean the cell dies completely
  44. what is mitotic death?
    • occurs when the cell dies after one or more divisions
    • can occur from very small doses
  45. what is mitotic delay? how much radiation?
    • the cell fails to divide on time
    • as little as 1 rad
  46. can radiation interfere with a cell's function? if so, is it permanent or temporary? can it be fixed?
    • yes
    • permanent or temporary
    • cell can recover and continue to funtion if repair enzymes are able to fix the damage
  47. which cells are very sensitive to radiation?
    • skin
    • intestinal crypt cells
    • reproductive cells
  48. which cells are radioinsensitive?
    • brain
    • muscle
    • nerve cells
  49. what other factors contribute to cell radionsentivity besides the cell's structure?
    • LET
    • presence of oxygen
    • cancer cells are often hypoxic- hyperbaric oxygenation of pts before treatment. makes them more sensitive to radiation
  50. what does law of bergonie and tribondeau state?
    • cells are the most sensitive if theyre:
    • youngest
    • least specialization or differentiation
    • graetest reproductive activity
    • longest mitotic phases
  51. what happens to the blood cells when the whole body is exposed to 25 rad?
    hematologic depression within a few days
  52. which cells are the most susceptible to radiation?
    lymphocytes or white blood cells
  53. how many rads will it take to depress the number of lymphocytes in circulating blood?
    25
  54. is the epithelial tissue radiosensitive or radioinsensitive? why or why not?
    • radiosensitive
    • it is constantly regenerated by the body
  55. are muscle tissue radiosensitive or radioinsensitive?
    radioinsensitive
  56. are nerve tissue radiosensitive or radioinsensitive?
    • radioinsensitive
    • highly specialized and do not divide
    • developing nerve cells are highly radiosensitive in the fetus
  57. how much radiation does it take to destroy the nervous system?
    5000 rads
  58. are reproductive cells radiosensitive or radioinsensitive?
    radiosensitive
  59. what can 200 rads do to reproductive cells?
    can cause temporary sterility for about a year in the male
  60. how much radiation can cause permanent sterility?
    500-600 rads
  61. how much radiation does it take to depress the sperm count?
    10 rads
  62. in the female, does the ova divide constantly?
    no
  63. how much radiation to the ovaries does it take to cause temporary sterility? permanent sterility
    • 200 rads temp
    • 500 rads perm
  64. how much radiation does it take to cause menstrual irregularities
    10 rads
  65. what would be the treshhold range to depress white blood cells?
    0-25 rads
  66. what would be the threshold range for temporary sterility?
    0-200 rads
  67. what does the linear nonthreshold curve estimate? what are some examples?
    • estimates the risk of associated with low-level radiation
    • leukemia, breast cancer, heritable damage
  68. what is the linear-threshold curve used for?
    nonstochastic effects such as skin erythema and hematologic depression
  69. what does the non-linear threshold curve determine?
    • used to determine high dose response in radiation therapy
    • indicates the existence of a threshold
    • for ex:
    • cataracts and blindness: once pt is blind, even higher radiation can no longer do damage to the eyes because it recieved the max damage
  70. what factors determine somatic and genetic damage?
    • quantity of radiation recieved
    • ability of ionizing radiation
    • amount of body area exposed
    • specific body parts exposed
  71. What can cause the greatest amount of biologic damage?
    • large dose of high LET delivered to a large or radiosensitivity area of the body
    • for ex: 1000 rads of alpha particle to the gonads is more damaging than 1000 rads of alpha to the head

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