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Year 3 Radiography > Risk and Dose > Flashcards

Risk and Dose Flashcards

1
Q

what is meant by absorbed dose (D) and unit

A

measure of amount of energy absorbed from radiation beam per unit mass of tissue, Gray (Gy, 1 Joule/kg)

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2
Q

explain how absorbed dose can vary in effect even if it is the same amount

A

depends how the energy is packaged: more damaging if energy fired in one go

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3
Q

explain equivalent dose (H) and units

A

allows potential harm from different types of radiation to be considered
H= absorbed dose (D) x radiation weighting factor (Wr)
unit= sievert (Sv)

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4
Q

radiation weighting factor (Wr) for

a) X-rays and gamma rays
b) beta particles
c) protons and neutrons
d) alpha particles

A

radiation weighting factor (Wr) for

a) X-rays and gamma rays: 1
b) beta particles: 1
c) protons and neutrons: 5-10
d) alpha particles: 20

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5
Q

interpret the radiation weighting factor of x rays and gamma rays

A

equivalent dose in sieverts= absorbed dose in Grays

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6
Q

explain effective dose (E) and unit

A

allows doses from different investigations or different parts of body to be compared, because some parts of body more radiosensitive than others
effective dose= dose equivalent x tissue weighting factor (Wt) (sieverts)
if more than 1 organ exposed, effective dose is sum of all effective doses to all exposed organs

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7
Q

what is the most radiosensitive part of the body?

A

gonads

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8
Q

what do each of these dosimetry abbreviations stand for:
D
H
E

A

D: absorbed dose
H: equivalent dose
E: effective dose

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9
Q

what medical examination gives the highest radiation dose?

A

CT chest

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10
Q

what medical examination gives the lowest radiation dose?

A

dental intraoral film

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11
Q

how long would it take to receive equivalant dose from background radiation compared to effective dose of intraoral x rays?

A

16 hours

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12
Q

how long would it take to receive equivalant dose from background radiation compared to effective dose of dental panoramic film?

A

3 days

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13
Q

how many mSv from

a) flight to Spain return
b) UK average
c) Cornwall
d) intraoral x rays
e) oral panoramic
f) chest x ray
g) head CT
h) barium meal
i) chest CT
j) mammography

A

a) flight to Spain return: 0.02mSv
b) UK average: 2.6 mSv/yr
c) Cornwall: 7.8mSv/yr
d) intraoral x rays: 0.001-0.008mSv
e) oral panoramic: 0.02mSv
f) chest x ray: 0.02mSv
g) head CT:2mSv
h) barium meal:3mSv
i) chest CT:8mSv
j) mammography:1.24mSv

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14
Q

risk of malignancy from 1 intraoral film using

a) traditional x-ray set and D-speed film
b) 70kV x-ray set and E-speed film

A

a) traditional x-ray set and D-speed film: 1/ 2 million

b) 70kV x-ray set and E-speed film: 1/20 million

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15
Q

risk of malignancy from 1 panoramic film

multiplication risk factors for age groups

A

0.21-1.9/ 1 million

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16
Q

explain collective dose

A

total effective dose to population
collective dose = effective dose x population
unit= man-Sv

17
Q

3 groups of population for purposes of limiting radiation dose

A

patients
occupationally exposed (workers)
general public

18
Q

4 things to consider before prescribing pt an x ray

A
  1. correct assessment of indications
  2. expected diagnostic yield (how useful is x ray)
  3. way in which results influence diagnosis/ treatment
  4. clinician having adequate knowledge of physical properties and biological effects of ionising radiation
19
Q

2 classifications of radiation workers

A

classified (>6mSv / year)

non-classified

20
Q

what are comforters and carers and dose limits

A

people who willingly undergo radiation exposure to support/ comfort pt, eg parent or carer
no dose limits but dose constraints

21
Q

3 golden rules of dose reduction

A

distance
shielding
time

22
Q

distances of controlled area

A

1m for sets up to 70kV
1.5m for sets above 70kV
(preferably operator >2m away from pt and x ray tube, not in line of primary beam)

23
Q

what law of physics does radiation follow? explain

A

inverse square law

intensity of radiation reduces to 1/4 as distance is doubled

24
Q

other rules of controlled area

A
  • warning light illuminated when x ray on

- warning notice provided when controlled area extends to door

25
Q

4 materials used for shielding

A
  1. lead
  2. lead rubber/glass
  3. concrete
  4. barium plaster
26
Q

2 ways to reduce dose to operator and comforter/ carer

A
  1. stand behind lead glass screen

2. lead-rubber apron

27
Q

when to use thyroid collars

A

if thyroid gland in primary beam

28
Q

what is collimation?

A

x ray beam shaping to minimum required to cover image receptor

29
Q

6 ways to use dental x ray set to reduce x ray dose

A
  1. higher kV (60-70kVp)
  2. rectangular collimation
  3. adequate aluminium filtration
  4. long focus to skin distance (>20cm)
  5. accurate timer
  6. adequate warning signals
30
Q

how to reduce dose by quality assurance

A
  • regular checks of equipment (x-ray and processing)

- image quality evaluation and audit

31
Q

advantage of digital imaging over film 5

A
  1. quicker
  2. less pt dose
  3. less storage requirements
  4. constantly evolving
  5. environmentally better
32
Q

2 dose measurements in radiography

A
  1. entrance surface dose (ESD) miliGrays, mGy. max dose to tissues, measured using thermoluminescent dosimeters (TLDs), ionisation chambers
  2. dose-area product (DAP): max dose to tissues
33
Q

who should have personal dosemeters?

A

people exposed to more than 1mSv/year

>100 intraoral or 60 panoramic films per week

34
Q

how do film badges work

A

contain photographic film to show how much radiation youve been exposed to

35
Q

advantages and disadvantages of film badges

A

advantages:
- cheap
- permanent record
- may be reassessed
- can see type of radiation received

disadvantages:
-processing required

36
Q

how do thermoluminescent dosimeters (TLD) work?

A

lithium fluoride crystals release stored radiation energy as light when heated

37
Q

advantages and disadvantages of TLDs

A

advantages:

  • sensitive
  • reusable
  • provide quick read-out
  • no processing required

disadvantage:

  • destructive read-out
  • expensive
  • limited info on energy of radiation received

Year 3 Radiography (9 decks)

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