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RD3033 > Topic 9: radiation dosimetry > Flashcards

Topic 9: radiation dosimetry Flashcards

1
Q

how much radiation comes from medical in the UK

A

12%

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2
Q

what are the dominant interactions between XR and gamma ray photons and tissue

A
  • photoelectric absorption
  • Compton scattering
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3
Q

4 possibilities of effects of radiation on DNA

A
  • no damage
  • fully repaired damage to one DNA strand
  • faulty repair of one DNA strand
  • beyond repair - cell death
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4
Q

3 types of radiation effects

A
  • somatic
  • genetic
  • teratogenic
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5
Q

stochastic effects of radiation

A
  • risk of effect occuring increases with dose but severity doesnt
  • effects may take years to show
  • involves DNA mutation but not cell death
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6
Q

deterministic effects of radiation

A
  • predictable
  • occur only above threshold dose which is high
  • severity increases with dose above threshold
  • effects usually occur quickly
  • often involves cell death
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7
Q

radiation teratogenesis

A

effects on embryo or fetus in utero

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8
Q

younger people are more at risk to radiation because

A
  • their cells are dividing faster
  • they will live longer giving more time for cancer to appear
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9
Q

what is dosimetry

A

measurement of dose caused by radiation deposited in a medium

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10
Q

importance of dosimetry

A
  • monitoring of exposures
  • identification of variation
  • legislation
  • protection of pts and staff
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11
Q

X

A

exposure

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12
Q

K

A

kerma

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13
Q

D

A

absorbd dose

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14
Q

Ht

A

equivalent dose

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15
Q

E

A

effective dose

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16
Q

what measure is intensity

A

measure of the number of photons in the beam

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17
Q

what does air ionisation chamber measure

A
  • measures exposure (X) in C/Kg and can also measure absorbed dose in air
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18
Q

KERMA

A
  • kinetic
  • energy
  • released
  • mass of
  • absorber
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19
Q

KERMA unit

A

1K = 1 Joule/ Kg

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20
Q

absorbed dose

A
  • measure of average energy absorbed from the radiation beam into medium
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21
Q

what is the stage 1 process of KERMA and absorbed dose

A

ionising photons transfer some of their energy to particles within mass and cause ionisation and charges particles
(KERMA, K)

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22
Q

what is stage 2 of the process of kerma and ABSORBED DOSE

A

the charged particles deposit their energy within the mass (absorbed dose)

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23
Q

where does the incoming energy from X-ray or gamma ray photons go?

A
  • part is used to create ion pairs
  • part is transfer to kinetic energy of the electron
24
Q

what does WR (weighting factor) account for

A

relative damaging effects of different types of radiation

25
Q

what is effective dose

A

sum of equivalent dose for all organs/ tissues weighed by a detriment-related tissue weighting factor

26
Q

what does the ICRP publication define tissue weighting factor to take into account

A

how radiosensitive each organ is

27
Q

important properties of radiation dosimeters

A
  • linear response
  • wide dynamic range
  • high sensitivity
  • high specificity
  • accuracy
  • isotropy (not affected by direction of incoming radiation)
  • fast response
  • low background noise
  • versatile
  • reusable
  • energy-dependent response
28
Q

the two type of dose-meters

A
  • absolute
  • practical
29
Q

features of absolute dose meters

A
  • very specialised equipment and techniques
  • kept at the national physical laboratory (NPL)
  • used under carefully controlled conditions
30
Q

features of practical dose-meters

A
  • smaller, more compact
  • used in hospitals/ universities
  • calibrated regularly against absolute dose-meter
  • sensitive to external factors, e.g. pressure
31
Q

types of dose meters

A
  • air-filled ionisation chambers
  • solid state detectors
  • radiographic film
32
Q

what do air-filled ionisation chambers do

A
  • measure charge created in a known volume of air
33
Q

what do air-filled ionisation chambers measure

A

measure exposure (X) which infers D and K

34
Q

examples of applications of air ionisation chambers

A
  • as detectors in automatic exposure devices
  • measure exposure (X) accurately
  • measure xr output and perform QA test on XR equipment
35
Q

how much energy is needed to create ion pair in air

A

34 eV

36
Q

what kind of process is creating an ion pair in an pair in air ionisation chambers

A

enclosed volume of air

37
Q

applications of semiconductor detectors

A
  • field dosimetry
  • quality control
  • personnel monitoring
38
Q

what are semiconductors used for

A

used to monitor staff exposure in interventional procedures

39
Q

advantages of semiconductor detectors

A
  • wide dynamic range
  • high sensitivity
  • small footprint allow excellent spatial resolution
  • fast response
  • versatile
40
Q

disadvantages of semi conductor detectors

A
  • energy dependent
  • expensive
  • sensitive to environmental conditions (temperature)
41
Q

what are TLDs

A
  • thermoluminescent dosimeters
  • passive dosimeters
42
Q

how do TLDs work?

A
  • some crystals absorb radiation energy when exposed to radiation and absorb it for long periods of time
  • this energy stored is released by heating the crystal
  • amount of light emitted is proportional to absorbed dose
  • calibration of TLDs allows absorbed dose to be determined
43
Q

advantages of TLDs

A
  • wide dynamic range
  • high sensitivity
  • reliable
  • small in size
  • reusable
  • versatile
  • no saturation
  • clean and quick processing
44
Q

disadvantages of TLDs

A
  • passive
  • storage instability
  • fading
  • light sensitivity
  • cant identify type of radiation
  • requires dedicated equipment
45
Q

what does radiographic film contain

A

contains an emulsion that absorbs radiation energy and stores it permanently
- chemical processing reveals this energy stored as optical density

46
Q

advantages of radiographic film

A
  • permanent record
  • can determine quality of radiation with filters
  • identify gross non- uniformities
  • visual inspection
47
Q

disadvantages of radiographic film

A
  • limited dynamic range
  • non-linear response
  • energy-dependent
  • wet chemical processing
  • fogging
  • doses unreliable in cases of gross overexposure
48
Q

the main purpose of a personal dosimetry programme

A
  • assess whether or not the exposure received by staff exceeds the dose limits
  • assess the effectiveness of strategies being used for dose optimisation
49
Q

challenges in measuring dose

A
  • measuring absorbed dose in tissues is not feasible
  • effective dose is an abstract quantity and for a population and should not be used to describe individual experience
50
Q

Hp (10)

A

effective dose ( whole body )

51
Q

Hp (3)

A

dose to lens of the eye

52
Q

Hp (0.07)

A

dose to the skin

53
Q

what is Hp (d)

A
  • quantity defined in the body
  • also cannot be measured directly
  • vary from person to person
  • vary according to location on the body where it is measured
54
Q

what is absorbed dose measured in

A

grays

55
Q

what is equivalent dose measured in

A

sieverts

56
Q

what is equivalent dose

A

the sum of absorbed doses from different types of radiation to a particular organ or tissue multiplied by respective radiation weighting factors

57
Q

what is effective dose

A

sum of equivalent doses to tissues/ organs irradiated X their respective tissue Weighting factors

RD3033 (15 decks)

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