4. Tissue Response to Radiation Flashcards
what is the equivalent dose
absorbed dose weighted for relative biological effectiveness
what units is the equivalent dose measured in
sieverts (Sv)
what are the weighting factors for x-ray/gamma/e-, neutrons, protons, and alpha particles
x-rays = 1 protons = 2 neutrons = 2.5-20 alpha = 20
what is the difference between equivalent dose and absorbed dose
no difference, just different units
what is the effective dose
equivalent dose weighted for biological sensitivity of tissues
what units is the effective dose measured in
Sieverts (Sv)
how do you calculate the effective dose for various tissues
what should it add up to
take tissue weighting factor and multiply by equivalent dose in Sv and add it up for different tissue categories
add up to 100% or 1.0
what is radiation damage
ionising radiation causes damage molecules that regulate cell processes
what happens in terms of repair occur when there are low doses
cell repair can rapidly occur
what happens in terms of repair occur when there are high doses
cell death results
what happens in terms of repair occur when there are extremely high doses
cells cannot be replaced quickly enough
out of the following rank them from most to least sensitive to radiation
skin, reproductive organs, blood forming organs, nervous system, muscle
most blood forming organs reproductive organs skin bone and teeth muscle nervous system least
what is the latent period
time between radiation exposure and the appearance of an effect
Initial effects subdue for a while during latent period but later there is increase in manifest illness
the latent period falls between what two stages in terms response
between early response and late response
what does the latent period depend on and how does it affect it?
dose
higher dose = earlier acute response
what is the predromata and how long dose it last
early effect and it is diminished during latent period (hr-wks)
as dose increases, the onset of effects gets ___ but severity of defects ___
shorter
increases
what are deterministic and stochastic effect
deterministic = tissue reactions
stochastic = chance damage
for deterministic effects
what is its dose levels how long is its latency period does it have a threshold dose what is its biological mechanism sample clinical effects
med-high dose short (days-weeks) latency period yes it has a threshold dose predominantly cell death mechanism skin lesions, cataract
for stochastic effects
what is its dose levels how long is its latency period does it have a threshold dose what is its biological mechanism sample clinical effects
low dose long (years) latency period no it does not has a threshold dose predominantly cell damage mechanism cancer, inherited defect in offspring
what do deterministic and stochastic effects depend on in its severity
deterministic = respond to certain dose
stochastic = severity is the same but risk changes based on factors eg age, gender, risk factors
what is the difference between somatic and hereditary/germline effects
Somatic cell = single cell, only affects one organ/part of tissue, not inherited
Germline = gametes, carried by whole body
what are examples of deterministic effects
acute radiation sickness milky lens/cataracts blood forming deficiency permanent infertility cell death skin lesions/burns hair loss
what are examples of stochastics effects
cancer
what does the dose response model assume
that the long term biological damage (ie cancer risk) is directly proportional to dose
evidence of increased risk of cancer is about ____ mSv in the dose response model
why dont we know the lower limit
100mSv
Cant do experiment as unethical and low end has background radiation as well so trend could be anything for lower limit
what are the 4 great line extrapolations for the linear no threshold model
supra-linearity
linear-quadratic
linear threshold
hormesis
how many grays constitutes as mild radiation exposure
1-2Gy
how many grays constitutes as moderate radiation exposure
2-6Gy
how many grays constitutes as severe radiation exposure
6-8Gy
what is acute radiation syndrome (radiation sickness)
result of receiving a large amount of ionising radiation in a very short time
what are some early symptoms of radiation sickness
nausea and vomiting
dizziness
headache
fever
what are some later symptoms of radiation sickness
dizziness and disorientation weakness, fatigue hair loss blood in vomit and stool infections, poor wound healing low blood pressure
For severe/higher doses the time taken for early effects to develop ___ and the Latent period also gets very ____, get effects ____
shortens
shorter
early on
what is the mean lethal dose
amount of ionising radiation taht will kill 50% of a population in a specified time
as the mean lethal dose increases what happens to how the proportion of the population is affected
As dose goes up the effects are not too significant but larger dose is affecting larger proportion of pop
