The flashcards below were created by user
swtjo3joe
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most effects of radiation begin where?
atomic level
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most effects of radiation manifests where?
cellular level
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chemical and biological effects are determined by the degree of what within the tissue?
ionization
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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
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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
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high or low LET radiation is more likely to interact with DNA
high
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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
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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
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what does LET and RBE pertain to?
radiation
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what does OER pertain to?
the tissue being irradiated
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what type of molecules does direct action pertain to?
- master molecules
- dna
- rna
- enzymes
- proteins
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what type of radiation interactions can occur during a direct action?
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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
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what is indirect action?
interaction of x-ray photons w/ non master molecules mostly water
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what is an example of indirect action?
radiolysis of water- xray hitting a water molecule
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radiolysis of water produces what types of ions?
- a positive water molecule HOH+
- an electron
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how many different reactions can occur after radioloysis of water (HOH+, e-)?
3
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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
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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
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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
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what is indirect action?
the damage caused by the byproduct of radiation (ions) with the macromolecule, not the radiation itself
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what is one of the main precursors of indirect action?
hydrolysis of water
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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
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what may result with point mutation?
gene mutations
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what type of LET radiation can cause point mutation (single strand break)?
low LET
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What type of LET radiation can cause a double strand break?
high LET
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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
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what causes cleaved chromosomes?
two interactions hit on each side of the sugar phosphate chain
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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
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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
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what is restitution?
- when a broken chromosome rejoins with the broken piece
- no damage
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what is deletion?
when a part of a chromosome is lost in the next division
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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
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what is target theory?
cell death will occur if the master molecule in that cell is inactivated by radiation exposure
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which theory is used to explain cell death and nonfatal cell abnormalities caused by radiation exposure?
target theory
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what happens if mutation is genetic?
- will be seen in future generations
- this is why we shield gonads
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what if mutation is somatic?
individual consequences only
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are radiation effects specific or nonspecific?
- nonspecific
- cant tell if an effect came from radiation or someting else
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are there certain cancers that are unique to radiation?
no
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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
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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
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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
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what is interphase death?
- interphase is cut short
- doesnt mean the cell dies completely
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what is mitotic death?
- occurs when the cell dies after one or more divisions
- can occur from very small doses
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what is mitotic delay? how much radiation?
- the cell fails to divide on time
- as little as 1 rad
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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
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which cells are very sensitive to radiation?
- skin
- intestinal crypt cells
- reproductive cells
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which cells are radioinsensitive?
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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
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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
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what happens to the blood cells when the whole body is exposed to 25 rad?
hematologic depression within a few days
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which cells are the most susceptible to radiation?
lymphocytes or white blood cells
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how many rads will it take to depress the number of lymphocytes in circulating blood?
25
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is the epithelial tissue radiosensitive or radioinsensitive? why or why not?
- radiosensitive
- it is constantly regenerated by the body
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are muscle tissue radiosensitive or radioinsensitive?
radioinsensitive
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are nerve tissue radiosensitive or radioinsensitive?
- radioinsensitive
- highly specialized and do not divide
- developing nerve cells are highly radiosensitive in the fetus
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how much radiation does it take to destroy the nervous system?
5000 rads
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are reproductive cells radiosensitive or radioinsensitive?
radiosensitive
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what can 200 rads do to reproductive cells?
can cause temporary sterility for about a year in the male
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how much radiation can cause permanent sterility?
500-600 rads
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how much radiation does it take to depress the sperm count?
10 rads
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in the female, does the ova divide constantly?
no
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how much radiation to the ovaries does it take to cause temporary sterility? permanent sterility
- 200 rads temp
- 500 rads perm
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how much radiation does it take to cause menstrual irregularities
10 rads
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what would be the treshhold range to depress white blood cells?
0-25 rads
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what would be the threshold range for temporary sterility?
0-200 rads
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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
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what is the linear-threshold curve used for?
nonstochastic effects such as skin erythema and hematologic depression
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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
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what factors determine somatic and genetic damage?
- quantity of radiation recieved
- ability of ionizing radiation
- amount of body area exposed
- specific body parts exposed
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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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