Cell Cycle
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Sequence of activities that take place in a cell that leads to duplication of
DNA and division of a cell into two daughter cells.
Some cells at adulthood no longer reproduce and thus no longer cycle.
Have Does Dose Fractionation Help?
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, Allow time for normal cells to repair.
Minimize early response of radiation dose damage.
Maximizes Radiation Therapeutic Index.
Allows for the greatest therapeutic benefit without resulting in
unacceptable radiation side-effects.
Free Radicals
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Are atoms or molecules that have an unpaired electron in their valence
(outer most) shell.
They are not selective when looking for another electron to pair up with its
unpaired valence electron.
Many arise normally during biochemical reactions taking place in a cell.
Normally the body can take of free radicals until they
become excessive.
Mutations
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Damaged cell is incorrectly repaired and passed on. (Transformed cell -
cancer)
Linear Energy Transfer (LET)
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, Is the average energy (dE) deposited by ionization events traveling a set
distance (dl).
Indirect Effect
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Radiation interacts with other atoms/molecules to produce free radicals
which then damage DNA
~80% of cell is water
~2/3 of DNA damage due to hydroxyl radical
Indirect Effect - Radiolysis of Water
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Dose Rate Dependent
H2O2 (hydrogen peroxide) is a known byproduct of the radiolysis of water
is cells producing the indirect effect of radiation cellular damage.
Experiments have shown that the rate of H2O2 production is dose rate
dependent.
So not only is high dose rate exposure producing more ssb and dsb that
can be repaired, it is also producing a larger number for free radicals per
equal dose.
Potentially Lethal Damage
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, Ionization damage which is lethal unless modified and repaired by the cell.
Major ARS Clinical Characteristics
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Prodromal - immediate, > 1- 3 hours)
Latent - no symptoms, day(s)
Manifest (clinical) illness (HPS, GIS, CNS) - days, weeks, months
Recovery or death - days to weeks
Parts of a Typical Cell Survival CurveParts of a Typical Cell Survival Curve
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Usually plotted on semi-log graph paper
D0 = dose to reduce survival to 37%.
n = extrapolated number was first thought to mean the number of targets in
a cell.
Dq = quasi-threshold
Cataracts
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Lens of the eye dose greater than 10 Gy cataracts develop in nearly 100% of
the individuals. Latent period ranges from 5 to 30 years.
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Sequence of activities that take place in a cell that leads to duplication of
DNA and division of a cell into two daughter cells.
Some cells at adulthood no longer reproduce and thus no longer cycle.
Have Does Dose Fractionation Help?
Give this one a try later!
, Allow time for normal cells to repair.
Minimize early response of radiation dose damage.
Maximizes Radiation Therapeutic Index.
Allows for the greatest therapeutic benefit without resulting in
unacceptable radiation side-effects.
Free Radicals
Give this one a try later!
Are atoms or molecules that have an unpaired electron in their valence
(outer most) shell.
They are not selective when looking for another electron to pair up with its
unpaired valence electron.
Many arise normally during biochemical reactions taking place in a cell.
Normally the body can take of free radicals until they
become excessive.
Mutations
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Damaged cell is incorrectly repaired and passed on. (Transformed cell -
cancer)
Linear Energy Transfer (LET)
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, Is the average energy (dE) deposited by ionization events traveling a set
distance (dl).
Indirect Effect
Give this one a try later!
Radiation interacts with other atoms/molecules to produce free radicals
which then damage DNA
~80% of cell is water
~2/3 of DNA damage due to hydroxyl radical
Indirect Effect - Radiolysis of Water
Give this one a try later!
Dose Rate Dependent
H2O2 (hydrogen peroxide) is a known byproduct of the radiolysis of water
is cells producing the indirect effect of radiation cellular damage.
Experiments have shown that the rate of H2O2 production is dose rate
dependent.
So not only is high dose rate exposure producing more ssb and dsb that
can be repaired, it is also producing a larger number for free radicals per
equal dose.
Potentially Lethal Damage
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, Ionization damage which is lethal unless modified and repaired by the cell.
Major ARS Clinical Characteristics
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Prodromal - immediate, > 1- 3 hours)
Latent - no symptoms, day(s)
Manifest (clinical) illness (HPS, GIS, CNS) - days, weeks, months
Recovery or death - days to weeks
Parts of a Typical Cell Survival CurveParts of a Typical Cell Survival Curve
Give this one a try later!
Usually plotted on semi-log graph paper
D0 = dose to reduce survival to 37%.
n = extrapolated number was first thought to mean the number of targets in
a cell.
Dq = quasi-threshold
Cataracts
Give this one a try later!
Lens of the eye dose greater than 10 Gy cataracts develop in nearly 100% of
the individuals. Latent period ranges from 5 to 30 years.
