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what is linear energy transfer
when passing through something ionizing radiation may interact with it during its passage and as a result deposits energy along its track
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what is an important factor in assessing potential tissue and organ damage from exposure to ionizing radiation
LET
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what is considered low LET
low let causes damage through what kind of interactions
- electromagnetic radiation like xrays and gamma rays
- indirect interactions
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what are repair enzymes
they reverse cellular damage to dna from radiation
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high LET radiation do not _______ far but cause ______ ionizations in a shorter length of track
when is high let of great concern
when it is ingested inhaled or radionuclide implanted
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high let does what damage to DNA
irrepairable damage caused by multiple strand breaks
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What is RBE and what does it stand for
when LET increase what also increases
- relative biologic effectiveness
- it is the capabilities of radiation with differing LET's to produce a particular biologic reaction
- RBE
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what is OER and what does it stand for
- oxygen enhancement ration
- oxygen enhancement ratio is numerical value of the ratio of radiation dose required to cause a particular biologic response of cells or
- organisms in an oxygen deprived environment to the radiation dose required to cause an identical response under normal oxygenated conditions
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why does oxygen in biologic tissue makes the damage produced by an indirect action permanent
because O2 combines with free radical to produce organic peroxide compounds
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damage to what cells can result in genetic mutations
germ cells
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most interactions that are involved with ionizing radiation are ______?
another term for an indirect interactions with radiation is ______
- indirect interactions
- radiolysis
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what happens during a direct action
the damage results from ionization of atoms on master molecules leading to inactive or dysfunctional molecules
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what is an indirect action
is caused by the interaction of free radicals with water molecules (radiolysis) which in turn disrupt the master molecule and lead to cell death
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two free radicals (OH) can combine to form what and are poisonous (toxic) to the cell
H202 hydrogen peroxide
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what is a single strand break and when is it commonly associated with
- energy transferred from ionizing radiation to a DNA molecule can break one of the chemical bonds on one side of the sugar phosphate side rail
- associated with low let radiation (gamma and xray)
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double strand breaks occur during what type radiation
what is a double strand break
- high let radiation
- multiple strand breaks in the sugar phosphate side rails
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what is double strand break in the same rung of the DNA
a broken chromosome
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what is mutation
ex?
- is the loss or change in a nitrogenous base in the DNA chain
- which causes incorrect information being sent over to the daughter cells
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what are covalent links
are chemical unions create between atoms by the single sharing of one or more pair of electrons
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what are the possible effects of ionizing radiation on chromosomes
restitution - breaks rejoin with no visible damage deletion - part of chromosome is lost at the next division broken end arrangement - misshape chromosome produced broken end rearrangement - genetic material is rearranged damage not visible results in mutation
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what is the target theory
the belief that there is a master or key molecule in the cell(DNA) and that it is necessary for the ssurvival of the cell
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when can the target theory be deactivated
when exposed to ionizing radiation
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what are the cellular effects of irradiation(7)
- instant death
- reproductive death
- apoptosis (interphase death) - occurs normally
- mitotic or genetic death
- mitotic delay
- interference of function
- chromosome breakage
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what is instant death
how much Gy is associated with it
does this occur in diagnostic and therapeutic range
- happens when a large volume is irradiated with a dose of 1000GY(100000 RADS) in a period of a few seconds or minutes a large number of cells will die instantly
- no
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what is reproductive death
when does it occur (how much Gy)
- occurs after doses of 1-10grays (100-1000rad)
- cell doesnt die it loses its ability to replicate and the damage is not transmitted to new generations of cells
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which areas of the body handle radiation better smaller or larger (whole body)?
smaller areas of the body
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what is apoptosis (programmed cell death)
what is it known as
when does it occur
- Nonmitotic the cell dies during interphase without attempting to divide
- interphase death
- spontaneously in normal tissue and tumors in humans
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what happens to the cell in apoptosis and what does it produce
what do blebs do
- cell shrinks and produces tiny membrane enclosed structures called blebs
- blebs break up cell and nucleus and ingest each other
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what amount radiation is need for apoptosis to occur in bone and lymphocytes and spermatogonia (meausred in Gy)
- bone = several thousand gy
- lymphocytes and sperm = few hundred gy
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what is mitotic (genetic) death
occurs when the cell dies after one or more divisions following inhibition of reproduction by radiation
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what is mitotic delay
when can this occur (level of dose)
- happens when the cell doesnt divide on time but can resume normal mitotic function
- small as 1 rad
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what is interference of function
it is temporary or permanent dependent on the ability of the repair enzymes to fix the damage
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the presence of what element promotes indirect damage through the formation of free radicals
o2
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what can be used to promote tumor radiosensitivity in order to destroy it
- a highly pressured (hyperbaric) oxygen setting or oxygen
- by increasing o2 in the capillaries of the tumor they become more sensitive and responsive to radiation
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where are hypoxic cells commonly found
why are the cells more difficult to destroy through indirect interaction
- in tumors
- because it has very low oxygen
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what is a chemical agent that can increase the radiosensitivity of a tumor
misonidazole
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what is the law of bergione and triboneau
radiosensitivity is directly proportional to reproductive activity and indirectly proportional degree of differentiation
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what cells and phases are most radiosensitive
immature cells are AKA?
- immature cells w/high reproductive activity and long mitotic phases
- unspecialized/undifferentiated cells
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unspecialized cells are cells that are _____
ex?
unspecialized are known as _____
- immature or constantly reproducing
- cells of embryo -fetus
- undifferentiation/immature
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Specialized/differentiated cells are ____
cells that do not reproduce as rapidly
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list radioresistant and radiosensitive cells
- radioresist. = bone muscle and nerve cells, sperm and egg (less sensitive than immature verison)
- radiosensitive = blood cells immature wbcs, spermagonia, oogonia (germ cells), intestinal crypt cells basal skin cells
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what is the worst break in the dna chain
base break
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what dose (Gy) of radiation will cause a measurable decrease in circulating blood cells
this does what to the stem cells
- 25 rad (.25gy
- causes a decrease in immature stem cells produced depletion increases as bone marrow dose increases
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what is LD-50/30
what is the LD expressed in humans and how much radiation is required in GY
stands for lethal dose required to produce death in 50% of the population in 30 days
- LD-50/60
- 300-400 RAD(3-4gy)
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what is the most radiosenstive cell in the body and what are they collectively known as
what are the three groups of lymphocytes
- Leukocytes or lymphocytes (wbc's)
- lymphocytes
- neutrohpils
- granulocytes
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what are the precursors to RBC's and what is their degree of sensitivity to radiation
mature blood cells are ______
- erythrocytes
- they are very sensitive
- less sensitive
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what are the other RBC's and their precursors
- megakaryoblasts = platelets (precursor)
- myeloblasts = granulocytes
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what is the typical wbc count in the body
5000-10000/mm3
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what is the function of lymphocytes and
defend body against antigens as depletion increases ability to fight infection decreases
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which cells has the shortest life span in 24 hrs of blood cells
which wbc manufactured where are most radiosensitive
- lymphocytes
- when manufactured in bone marrow
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why are patients platelt count monitored frequently in therapeutic dose imaging
because they recieve more radiation and these high doses cause decrease in blood count
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when do chromosomal aberrations occur in lymphocytes
- high level fluoro
- very long flouro exposure times
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list all epithelial tissue that are highly _____ and are ________ to radiation found where
- mitotic
- highly sensitive
- instestinal lining
- respiratory tract
- pulmonary alveoli
- blood and lymph vessel lining
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reproductive cells of the male and female are highly ______
sensitive
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what is the window of maximum sensitivity for pregnant women
8-15wks after gestation
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what dose of radiation results in a 4% chance of mental retardation
10 rem
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routing abdominal fluoro case will result in a fetal equivalent dose of ____
5rem
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mature spermatogonia are _______ to radiation
insensitive or more resistant
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a dose of _____ is enough to cause temporary sterility for 12 months
a dose of ______ is enough to cause permanent sterility
doses as low as _____ can do what to sperm count
- 200-300rad = 2-3 gy
- 500-600 rad = 5-6gy
- 10rad; depress
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what is fractioned and protraction doses
- fractioned doses are radiation received over a period of time or wks
- protraction doses radiation given at a single time over long amt of hours
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what the principle radiation effects on the embryo/fetus (list 3)
- loss of pregnancy
- mental retardation
- malformations
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