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RAD > Lecture 5: radiation sources, measurement & radiobiology > Flashcards

Lecture 5: radiation sources, measurement & radiobiology Flashcards

1
Q

What % of UK deaths per year are due to radiation sources?

A

1%

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2
Q

What % of cancer deaths are due to radiation sources?

A

4%

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3
Q

Of the UK population dose, what % of radiation is man-made and what % is environmental?

A

man-made: 17%

environmental: 83%

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4
Q

Of the UK population dose, what % of the man-made radiation is medical/dental?

A

medical/dental: 90%

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5
Q

Of the medical/dental exposures, what % is dental?

A

dental: 9%

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6
Q

What % of all x-ray examinations are dental?

A

dental: 30%
medical: 70%

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7
Q

Give 4 reasons why someone may receive an unnecessary x-ray dose?

A
  • no valid justification for it
  • incorrect radiation (60kV instead of 70kV)
  • using a round collimator instead of a rectangular one
  • having to repeat it
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8
Q

What 2 properties of x-rays can be used to measure the dose?

A
  • ionisation

- excitation

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9
Q

What are the 6 types of dose meters?

How do they each work?

A

1- Free air ionisation chamber (collects electrons and measure charge)

2-Thimble ionisation chamber (measures discharge due to ionisation)

3-Chemical conversion: Frickes’ Dose Meter (measures chemical change due to ionisation

4-Photographic density (assessed through level of black caused by ionisation of silver bromide)

5- Calorimetry (measures heating effect due to excitation)

6- thermoluminescent dose meter (assess dose by measuring released stored energy)

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10
Q

How does free air ionisation chamber work?

A
  • Two plates are parallel to each other (one single plate above -ve the other broken plate below +ve)
  • The arrangement of the charged plates produces a measurable volume between the plates. .
  • X rays hit 1kg of free air and electrons (carrying their negative charge) will move towards the +ve bottom plate
  • The electrons move through the bottom plate to a meter. Measuring the charge will indicate how many electrons and therefore, ionisation events took place.
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11
Q

What unit measures the amount of electrons/charge released?

A

Coulombs. It measures the charge transported by a constant current of one ampere in one second

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12
Q

How does a Thermoluminescence dose meter work?

A
  • It operates between the conduction band and valency band of atoms, known as the Forbidden zone
  • Exposure to radiation raises the energy level of the electrons and they are trapped in this Forbidden Zone, by ‘cups/traps’ known as energy anomalies
  • The energy given to the electrons is the exact same energy given to the patient
  • The electrons remain here until released by heating. As the electrons drop down from the ‘traps’ they release energy as light.
  • This light is picked up by a metre and can measure the dose. The intensity of the light released is proportional to the dose received
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13
Q

What are the advantages of Thermoluminescence dose meter?

A
  • can be reused
  • relatively cheap
  • wide range: capable of measuring very large & very small doses
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14
Q

What are the disadvantages of Thermoluminescence dose meter?

A
  • no permanent dose record

- sensitive to extreme environments (heat in particular)

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15
Q

What is Radiation Exposure?

unit?

A
  • Number of ionisation events

- C/kG

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16
Q

What is the absorbed dose?

unit?

A
  • total energy absorbed

- J/kg (Grays)

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17
Q

What is equivalent dose?

unit?

A
  • represents the stochastic health effects of low levels of ionizing radiation on the human body
  • Sieverts (Sv)
18
Q

What is the effective dose?

unit?

A
  • sum of the equivalent doses in all specified tissues and organs of the human body and represents the stochastic health risk to the whole body.
  • Sieverts (Sv)
19
Q

What is the equation to work out the effective dose?

A

absorbed dose (Gy) X radiation weighting factor (Wr) X Tissue weighting factor (ΣWt)

Gy X Wr X ΣWt

Gy X 1 X 15

20
Q

Which is the most important measurement?

why?

A
  • Effective dose

- Because it is the only measurement that gives a realistic assessment of the potential harm given to the patient

21
Q

How many individual weighting factors are there for tissue?

What are the top 3 most affected tissues?

A
  • 15

- ovaries/testes, stomach, intestines

22
Q

What are the 2 ways photon interactions can damage human tissue?

A
  • direct effects

- indirect effects

23
Q

How does direct human tissue damage occur?

A

When a photon interacts with a biological molecule

24
Q

How does indirect human tissue damage occur?

A

When a photon interacts with a water molecule

25
Q

What is the chemical process of radiation damage?

A

-Once the photon has interacted either directly/indirectly with a target molecule the chemical process is identical:

1- The molecule will become ionised
2-Ionisation causes dissociation of the molecule and the formation of free radicals
3-These free radicals produce abnormal chemical reactions

26
Q

What is more common in humans, indirect or direct damage?

Why?

A
  • Indirect damage is more common

- because we contain a lot of water (60-65%)

27
Q

What 3 effects can radiation damage have on the cells?

How likely is it to occur at a dental dose?

A

1- Cell death: not at dental dose

2- Prevention or delay in cell division: unlikely at dental dose

3- mutation: will occur at dental dose.

28
Q

Is there a threshold dose at which mutation occurs?

A

No, any radiation dose can cause mutation

29
Q

Within the cell, what can be affected?

A
  • DNA

- cytoplasmic organelles (mitochondria, centrioles, Golgi apparatus, smooth/rough ER)

30
Q

What are the 2 major effects of radiation exposure?

A
  • stochastic (random)

- deterministic

31
Q

What are the 7 features of stochastic effects of radiation exposure?

A

1- it is random/unpredictable
2-probability increases as dose increases
3-there is no tissue repair for damaged tissue
4-these effects are cumulative (since they don’t repair, the damage accumulates with every dose added)
5- severity is not dose related (related to which parts of the body becomes abnormal)
6-there is no threshold at which someone will definitely develop a tumour, and there is no threshold to guarantee no cancer
7-no safe waiting period between doses

-will arise from chronic exposure and can occur anywhere in the body at any time (months, years after)

32
Q

What are the features of deterministic effects of radiation exposure?

A

1-does have a degree of predictability
2-some tissue repair is possible between exposures
3-tissue damage does not accumulate
4-severity is dose related. The bigger the dose the worse the damage
5-there is some threshold to determine the extent of damage

  • will arise from acute exposure and will occur at localised areas where the tissue was exposed.
33
Q

When receiving an x-ray, what radiation effects are given?

A

both stochastic and deterministic effects

34
Q

What is a somatic effect?

A
  • the radiation effects that occur in the individual that has received the x-rays.
  • Can be stochastic or deterministic
35
Q

What is a genetic effect?

A
  • the radiation effects that occur in the offspring of the individual that received x-rays
  • only genetic effect if the exposure occurred BEFORE conception of the individual
  • stochastic
36
Q

Does the risk of genetic effects remain the same in all offspring of the affected individual?

A

No, the further genealogically from the affected individual the less likely the offspring are to present with genetic effects

37
Q

If a pregnant mother receives an x-ray and the baby develops cancer due to the exposure, is this somatic or genetic effects?

A

somatic effect. The baby was already conceived and had received their own dose of x-rays.

38
Q

Who is more at risk of radiation damage, children or adults?

A

children

Under 10 years the radiation is 2X more dangerous

39
Q

Why are children more at risk of radiation damage?

A

1- size: they are a lot smaller and will have less interstitial fluid

2- water content: children contain more water, so more likely to receive indirect effects

3- immune system: children don’t have a fully developed immune system

40
Q

What causes the severity of x-ray effects?

A

It is WHERE the abnormal effects are developed. (somewhere harmful: brain, lungs).

RAD (7 decks)

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