3.1/3.2 radiation health effects I&II Flashcards
to describe the health effects of exposure to ionizing radiation, what 3 things must we define?
- absorbed dose
- equivalent dose
- effective dose
what is the largest man-made source of radiation exposure to general population worldwide?
the radiation exposure from diagnostic X-rays
man-made exposure contributes ___% of total annual exposure from all sources
14
why is the concept of exposure significant?
because although diagnostic x-rays provide great benefits, their use involves some small risk of developing cancer
what is exposure (or exposure dose)?
- the method of measuring the amount of ionization in air
- measures the ratio of the total charge produced (of, electrons for example) in a small volume of air
what is the unit of exposure for air?
- Coulombs per kilogram (C/kg)
- Röntgen
(1R = 2.58 x 10^-4 C/kg)
what does exposure ONLY apply to?
X-rays and γ-rays (photons)
as a measure of radiation damage, exposure has been superseded by the concept of
absorbed dose
what is absorbed dose?
a quantity that better describes the effects on radiation on materials/human beings
what is the SI unit of absorbed dose?
the gray (Gy)
what is absorbed dose equivalent to?
- the absorption of one joule of energy in a kilogram of a substance by ionizing radiation
- (or amount of energy that is absorbed to the mass (matter) to the human body)
- (1 Gy = 1 J/kg)
since the Gray is a large unit, for radiation protection purposes, it is more common to use ____ and ____
- microgray (μGy) - (1 x 10^-6)
- milligray (mGy) - (1 x 10^-3)
what is KERMA?
- KINETIC ENERGY RELEASED IN MEDIUM
- when a photon beam interacts with a medium, the photon interactions release electrons with KE into the medium
the energy deposited by these electrons per unit mass is the?
absorbed dose
what is the unit for KERMA?
- joule per kilogram (same as absorbed dose)
when is KERMA dose equal to absorbed dose, and when is it different?
- different doses at high energies (up to 1 MeV)
- doses are roughly equal at low energies
_____ is energy released, and _____ is energy absorbed
KERMA, absorbed dose
what allows the effect of radiation exposure on human tissue to be determined?
equivalent dose
what do we use equivalent dose for?
to relate the absorbed dose in human tissue to the effective biological damage of ionizing radiation
explain why we might not get the same biological effects of the same amounts of absorbed doses?
- not all types of radiation has the same biological effect, even for the same amount of absorbed dose
- example: if we have equal amounts of absorbed dose of both X-rays and another organ that absorbed an α-particle, there won’t be equal biological effects of each
- since α-particles are much heavier, they cause more damage to cells
- it is important to take into account the type of radiation
in what cases do we use equivalent doses in?
when we need to take into consideration the different types of radiation
what is the SI unit of equivalent dose? what does it represent?
- the Sievert (Sv)
- it represents the stochastic biological effect (i.e. cancer)
the Sievert is also a large unit, for normal radiation protection levels, it is more common to use _____ and _____
- microSievert (μSv)
- milliSievert (mSv)
what equation do we use to determine equivalent dose?
HT = Σ WR x D
- HT - equivalent dose
- WR - radiation weighting factor
- D - absorbed dose
what is the use of radiation weighting factor (WR)?
it takes into account the type of radiation when making a calculation
(that some kinds of radiation are more dangerous to biological tissue)
how do we determine the dose in Sieverts from the dose in Grays?
multiply by the WR
what is the relationship between absorbed Sieverts in a unit of time and exposure intensity?
the more Sieverts absorbed in a unit of time, the more intense the exposure
(higher dose=higher intensity)
what is it called to express exposure as an amount over a specific amount of time?
dose rate
(ex: 5 mSv per year)
which dose quantity shows that the probability of a harmful effect from radiation exposure depends on the part(s) of the body exposed?
the effective dose
give an example that shows that some organs are more sensitive to radiation than others
bone marrow is a more dense organ compared to skin, so it can be damaged more easily than skin for the SAME amount of radiation
what equation do we use to determine effective dose?
E = Σ WT x HT
- E - effective dose
- WT - tissue weighting factor
- HT - equivalent
what is the use of tissue weighting factor (WT)?
it takes in account the sensitivity of each organ tissue when making a calculation
what is the SI unit of effective dose?
the Sievert (Sv)
(since equivalent and effective dose both use Sv, identify which you have used when calculating)
the higher the value of WT, the _____?
the higher the sensitivity of the organ tissue
list the 3 dose quantities
(1) absorbed dose: energy “deposited” in a kg of a substance by the radiation
(2) equivalent dose: absorbed dose weighted for harmful effects of different radiations (WR)
(3) effective dose: equivalent dose weighted for susceptibility to harm of different tissues (WT)
what are the annual dose limits for (1) occupational workers and (2) the public?
occupational workers - 20mSv
public - 1 mSv
what are the annual equivalent doses of
- lens of the eye
- skin
- hands & feet
- 20 mSv
- 500 mSv (occupational), 50 mSv (public)
- 500 mSv
why is ionizing radiation much more harmful than chemical or other physical agents?
- each ionization results in a small cluster of ion pairs
- each of these clusters represent a very small amount of energy (≈100eV per cluster)
- even small radiation exposures will create millions of ion pairs in the exposed tissues
- at the bimolecular level, the energy deposition is highly localized and non-uniform
relatively large volumes of each cell will receive ____ while, smaller volumes receive ____ when exposed to radiation
large volumes receive no energy at all while smaller volumes receive a higher dose
what happens to the location where ionization occurs?
the energy deposited is very high
how could a macromolecule become damaged by ionizing radiation without raising the temperature of the cell outside normal range?
- even very small doses (mGy) of ionizing radiation will produce a large number of random sub-molecular events in cells
- any one of these may damage a sensitive macromolecule
only about ___% of the ionization events are potentially harmful, because there are enough mechanisms of DNA repair
1%
what are the two ways radiation can attack DNA?
- direct route
- indirect route
describe the direct route of radiation attacking DNA
- in very high energies, radiation (photons) can directly attack DNA
- the relatively small negatively charged electrons can also cause damage by direct interaction with DNA
- heavier, more densely ionizing charged particles (α-particles) are much more likely to cause direct damage
describe the indirect route of radiation attacking DNA
- since the most abundant cellular molecule is water, radiation will mostly ionize H2O molecules
- this results in the formation of FREE RADICALS (hydroxyl, hydrogen)
- they are highly reactive and will re-combine to reform water
- however, if these radicals are formed within a few nm of large biological macromolecules/cell membranes/ cellular DNA, they could interact with them
- this indirect action, could initiate a chain of sub cellular events that will produce detectable changes in cells
- after low doses, free radical effects may lead to delayed but increased risks of cancer
- with higher doses, microscopic damage is even more severe
which radical is the most damaging of the free radicals?
the +OH˚radical
- it initiates about 2/3 of all the effects of external exposure of the body to X- or γ- rays
what are some effects of radiation exposure on DNA?
- single-stand break
- double-strand break
- base loss / base change
- cross-linkage
- DNA cross-linkage
- protein cross-linkage
what are the two categories of effects due to radiation?
- stochastic effects
- deterministic effects
