3.1/3.2 radiation health effects I&II

Question 1

to describe the health effects of exposure to ionizing radiation, what 3 things must we define?

Answer 1

• absorbed dose
• equivalent dose
• effective dose

Question 2

what is the largest man-made source of radiation exposure to general population worldwide?

Answer 2

the radiation exposure from diagnostic X-rays

Question 3

man-made exposure contributes ___% of total annual exposure from all sources

Answer 3

14

Question 4

why is the concept of exposure significant?

Answer 4

because although diagnostic x-rays provide great benefits, their use involves some small risk of developing cancer

Question 5

what is exposure (or exposure dose)?

Answer 5

• 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

Question 6

what is the unit of exposure for air?

Answer 6

• Coulombs per kilogram (C/kg)
• Röntgen
  (1R = 2.58 x 10^-4 C/kg)

Question 7

what does exposure ONLY apply to?

Answer 7

X-rays and γ-rays (photons)

Question 8

as a measure of radiation damage, exposure has been superseded by the concept of

Answer 8

absorbed dose

Question 9

what is absorbed dose?

Answer 9

a quantity that better describes the effects on radiation on materials/human beings

Question 10

what is the SI unit of absorbed dose?

Answer 10

the gray (Gy)

Question 11

what is absorbed dose equivalent to?

Answer 11

• 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)

Question 12

since the Gray is a large unit, for radiation protection purposes, it is more common to use ____ and ____

Answer 12

• microgray (μGy) - (1 x 10^-6)
• milligray (mGy) - (1 x 10^-3)

Question 13

what is KERMA?

Answer 13

• KINETIC ENERGY RELEASED IN MEDIUM
• when a photon beam interacts with a medium, the photon interactions release electrons with KE into the medium

Question 14

the energy deposited by these electrons per unit mass is the?

Answer 14

absorbed dose

Question 15

what is the unit for KERMA?

Answer 15

• joule per kilogram (same as absorbed dose)

Question 16

when is KERMA dose equal to absorbed dose, and when is it different?

Answer 16

• different doses at high energies (up to 1 MeV)
• doses are roughly equal at low energies

Question 17

_____ is energy released, and _____ is energy absorbed

Answer 17

KERMA, absorbed dose

Question 18

what allows the effect of radiation exposure on human tissue to be determined?

Answer 18

equivalent dose

Question 19

what do we use equivalent dose for?

Answer 19

to relate the absorbed dose in human tissue to the effective biological damage of ionizing radiation

Question 20

explain why we might not get the same biological effects of the same amounts of absorbed doses?

Answer 20

• 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

Question 21

in what cases do we use equivalent doses in?

Answer 21

when we need to take into consideration the different types of radiation

Question 22

what is the SI unit of equivalent dose? what does it represent?

Answer 22

• the Sievert (Sv)
• it represents the stochastic biological effect (i.e. cancer)

Question 23

the Sievert is also a large unit, for normal radiation protection levels, it is more common to use _____ and _____

Answer 23

• microSievert (μSv)
• milliSievert (mSv)

Question 24

what equation do we use to determine equivalent dose?

Answer 24

HT = Σ WR x D

• HT - equivalent dose
• WR - radiation weighting factor
• D - absorbed dose

Question 25

what is the use of radiation weighting factor (WR)?

Answer 25

it takes into account the type of radiation when making a calculation

(that some kinds of radiation are more dangerous to biological tissue)

Question 26

how do we determine the dose in Sieverts from the dose in Grays?

Answer 26

multiply by the WR

Question 27

what is the relationship between absorbed Sieverts in a unit of time and exposure intensity?

Answer 27

the more Sieverts absorbed in a unit of time, the more intense the exposure
(higher dose=higher intensity)

Question 28

what is it called to express exposure as an amount over a specific amount of time?

Answer 28

dose rate
(ex: 5 mSv per year)

Question 29

which dose quantity shows that the probability of a harmful effect from radiation exposure depends on the part(s) of the body exposed?

Answer 29

the effective dose

Question 30

give an example that shows that some organs are more sensitive to radiation than others

Answer 30

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

Question 31

what equation do we use to determine effective dose?

Answer 31

E = Σ WT x HT

• E - effective dose
• WT - tissue weighting factor
• HT - equivalent

Question 32

what is the use of tissue weighting factor (WT)?

Answer 32

it takes in account the sensitivity of each organ tissue when making a calculation

Question 33

what is the SI unit of effective dose?

Answer 33

the Sievert (Sv)
(since equivalent and effective dose both use Sv, identify which you have used when calculating)

Question 34

the higher the value of WT, the _____?

Answer 34

the higher the sensitivity of the organ tissue

Question 35

list the 3 dose quantities

Answer 35

(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)

Question 36

what are the annual dose limits for (1) occupational workers and (2) the public?

Answer 36

occupational workers - 20mSv
public - 1 mSv

Question 37

what are the annual equivalent doses of
- lens of the eye
- skin
- hands & feet

Answer 37

• 20 mSv
• 500 mSv (occupational), 50 mSv (public)
• 500 mSv

Question 38

why is ionizing radiation much more harmful than chemical or other physical agents?

Answer 38

• 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

Question 39

relatively large volumes of each cell will receive ____ while, smaller volumes receive ____ when exposed to radiation

Answer 39

large volumes receive no energy at all while smaller volumes receive a higher dose

Question 40

what happens to the location where ionization occurs?

Answer 40

the energy deposited is very high

Question 41

how could a macromolecule become damaged by ionizing radiation without raising the temperature of the cell outside normal range?

Answer 41

• 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

Question 42

only about ___% of the ionization events are potentially harmful, because there are enough mechanisms of DNA repair

Answer 42

1%

Question 43

what are the two ways radiation can attack DNA?

Answer 43

• direct route
• indirect route

Question 44

describe the direct route of radiation attacking DNA

Answer 44

• 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

Question 45

describe the indirect route of radiation attacking DNA

Answer 45

• 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

Question 46

which radical is the most damaging of the free radicals?

Answer 46

the +OH˚radical
- it initiates about 2/3 of all the effects of external exposure of the body to X- or γ- rays

Question 47

what are some effects of radiation exposure on DNA?

Answer 47

• single-stand break
• double-strand break
• base loss / base change
• cross-linkage
• DNA cross-linkage
• protein cross-linkage

Question 48

what are the two categories of effects due to radiation?

Answer 48

• stochastic effects
• deterministic effects