*** Lecture 10 Flashcards
radiation biology
study of the biological effect of ionizing radiation on tissue
biological effects of radiation
stochastic effects and deterministic which is acute
stochastic effects
late effects: cancer and hereditary
what does the probability and severity do with stochastic dose effects
probability increases with dose, but severity is independent of dose
deteministic effects
acute effects: erythema, cataracts, blood cell defects, acute radiation syndrome
what does the probability and severity do with deterministic dose effects
severity increases with dose, but probability is independent of dose
what is the most common way to get deterministic and what is the most common way to get stochaistic
deterministic-is from occupational, but there is not very often. Diagnostic X-rays are the most common for stochastic. There is a threshold for the deterministic effects
how does ionizing radiation deposit energy
excitation, ionization, thermal heating- largest but very small component
what produces chemical changes in the tissue
excitation and ionization, which produce biological effects
what are biological effects of radiation
delayed after a period of time
can you tell the difference between chemical or physical agents
no
what is the direct effect of radiation on the tissue
photon directly ionizes or excites a DNA molecule, which then DN< RNA< protein or enzyme is then ionized or excited
what is the indirect effect of radiation on the tissue
a reactive chemical is produced, which interacts with water and the majority of tissue is water. This produces free radiacals, which have an unpaired electron, so they are very reactive.
what can ROS form
water, which does nothing or it can form a hydrogen peroxide which is damaging to interact with macromolecules
what enhances ROS damage
O2
what predicts the severity of biological response
the cell function that is affected especially the cell division
what happens to cells with the most damage
they apoptosis, and eliminate future biological response
what is target theory
model of cell damage. a cell may be inactivated by a certain number of hits. A hit may be direct or indirect interaction. Cells have certain DNA that is not redundant. A hit to redundant molecules will not result in cell death
is dingle strange or double stranded breaks more common and what are they
single are more common and they are more easily repaired. The double stranded happen less frequently but are harder to repair
what two things can cause a mutation
base deletion or substitution
what happens to chromosomes when hit with radation
broken ends are sticky and and can rejoin with other broken ends, and this repair can lead to a whole mess
can lead to eccentric or miscombined with different translocations.
what are the aberrations present with the chromosomes
dicentric, acentric, ring
what can be used to estimate the amount of radiation received
the number of aberrations in human lymphocytes can be used to estimate the amount of radiation exposure received. Total body doses>.25gy can be detected many years later
cell radiosensitivity
used to evaluate the effect of radiation on cell proliferation under various conditions including different types of ration, environmental factors, different types of cells. Cells are grown in tissue culture the exposed to radiation then surviving colonies are counted. Cell survival curve shows fraction surviving versus dose
what is n
it is the extrapolation number between n2-10 and the number of hits required to inactivate cell or the number or critical targets in a cell
what is D0
1/slope indicates the general radio sensitivity of cells
what is a large D0 mean
it means there is a radioresistance
low D0 means what
radiosensistive
D0 is usually between
1-2 gy
Dq
threshold dose- width of the shoulder region. Measures ability of cells to recover from sublethal damage.
what is large Dq
cells can easily recover or low energy radiation
what factors effect the radio sensitivity of cells
dose rate, dose fractionation, radiation quality, oxygen, chemical protectiors, type of cell, stage of the cell cycle
dose rate and fractionantion
high dose rates cause greater amage. Fractionation of dose reduces the biological damage. Low dose rates and fractionation gives the cells time to reapiar
LET
linear energy transfer. high LET is alpha protons and high energy photons. Low LET means there is beta stuff and gamma rays
dose low or high LET cause more damage
high
does free O2 increase or decrease damage
increased cell damaged because there can be formation of products.
what do chemical protectors do
decrease cell damage and these chemicals scavenge free radiacls and add an H to help DNA repair like sulhydrl amifostine, but almost need it to be toxic
which cells have the greatest sensitivity
rpid devision, large number or future divisions, low differentiation, lymphocytes are radio resistant, but still kinda radiosensitive
what cell cycle is most sensitivie
during M and late G2 phase
what cell cycle phase is most resistant
late S phase