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Medical Imaging > Radiation Protection - Practical Aspects 1+2 > Flashcards

Radiation Protection - Practical Aspects 1+2 Flashcards

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USMLE® Step 1 flashcards
1
Q

When is dose area product used?

A

diagnostic radiology except CT

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2
Q

When is dose length product used?

A

CT

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3
Q

Purpose of DAP and DLP?

A

starting point to estimate patient effective dose

estimate scattered dose from patient

audit practice

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4
Q

How to calculate DAP?

A

x-ray beam area x absorbed dose

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5
Q

DAP is _______ with distance if there is no attenuation

A

invariant

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6
Q

Why are conventional ionisation chambers not appropriate to measure doses in CT?

A

due to geometry

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7
Q

What is used to measure doses in CT?

A

pencil ionisation chamber

TLD array

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8
Q

What does pencil ionisation chamber depend on?

A

exposure factors

beam width

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9
Q

What axis is the dose measured along in CT?

A

z axis

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10
Q

What are CT doses measured in? and with what unit?

A

air or phantom
mGy.cm

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11
Q

How is CT dose index measured?

A

for a single rotation using a pencil ionisation chamber

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12
Q

CTDI equation

A

CTDI = dose profile in mGy.cm/ nominal beam width

area under curve/T

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13
Q

CTDI unit

A

mGy

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14
Q

What does CTDI vol account for?

A

pitch, measured using a phantom

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15
Q

What is weighted CTDI?

A

1/3 CTDI at centre + 2/3 CTDI at periphery

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16
Q

why is weighted CTDI calculated?

A

measured for standard protocols

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17
Q

how is weighted CTDI related to CTDI vol?

A

CTDI vol = CTDI w/pitch

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18
Q

How is weighted CTDI measured?

A

measured in standard perspex phantom (head and body sizes) at mAs used for examination
Units mGy

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19
Q

dose length product equation

A

CTDI vol *L
where L is scanned length

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20
Q

what does dose length product relate to?

A

dose from complete examination

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21
Q

HSE advice for a risk assessment under IRR17?

A

Identify the hazards
Decide who might be harmed and how
Evaluate the risks and decide on precaution
Record your findings and implement them
Review your assessment and update if necessary

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22
Q

hierarchy of exposure controls

A

engineering controls - safety features and warnings - systems of work - ppe

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23
Q

what does I131 emit?

A

gamma and beta

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24
Q

employee annual effective dose limit?

A

20 mSv

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25
Q

employee equivalent eye lens dose limit?

A

20 mSv

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26
Q

employee skin averaged 1cm2 equivalent dose limit?

A

500 mSv

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27
Q

employee extremities equivalent dose limit?

A

500 mSv

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28
Q

Classified person

A

employee likely to annually exceed:

6mSv effective dose
15mSv eye lens equivalent dose
150mSv extremity equivalent dose

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29
Q

What special requirements exist for classified persons?

A

dose monitoring, record keeping, medical surveillance

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30
Q

What devices are used to estimate staff doses?

A

thermo luminescent dosimeters
optically stimulated luminescent dosimeters
variety of electronic devices

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31
Q

When should monitors be approved for use by HSE?

A

if used by classified worker

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32
Q

What does effective dose monitoring measure?

A

Hp(10) body dose, Hp(0.07) skin dose

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33
Q

Where should effective dose monitoring devices be worn?

A

between shoulders and waist, under protective clothing

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34
Q

What do eye monitors measure?

A

estimate Hp(3) commonly using TLD

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35
Q

What types of eye monitors exist?

A

forehead or clipped to glasses on eye closest to source
collar outside of protective clothing

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36
Q

What do extremity monitors measure?

A

Hp(0.07) skin dose commonly with TLD

37
Q

Where are extremity monitors attached?

A

ring, finger stalls, bracelet

wear dose meter on digit which will receive max dose

38
Q

What is the ratio between the tip and base of the finger?

A

4-6

39
Q

What is the dose investigation level?

A

effective dose level set by employer and given in local rules
when the level is exceeded a review of working conditions is required to ensure doses are ALARP

40
Q

What is a typical dose investigation level?

A

1-4 mSv depending on work

41
Q

What can the DIL not exceed?

A

15mSv

42
Q

who should be notified if the DIL is exceeded?

A

HSE (health and safety executive)

43
Q

How should a DIL be set?

A

lower than dose limit - aim to keep doses ALARP

annual level required - monthly not

can set for equivalent doses too but not required

44
Q

How are DIL’s implemented?

A

staff monitored on monthly or quarterly basis depending on risk
ensure doses reviewed throughout the year so that excess can be identified

45
Q

Other reasons for high doses?

A

badge lost/dropped in controlled areas

exposed during travel/ medical exposure

deliberate exposure

46
Q

Increasing distance by ____ reduces effective dose by ~ half

A

30cm

47
Q

% change in dose increasing Pb apron 0.25mm to 0.5mm

A

few %

48
Q

why are thyroid shields used?

A

thyroid is particularly radiosensitive

49
Q

0.35mm Pb reduces effective dose by ___ times

A

at least 5

50
Q

eye dose limit reduced to ____ with eye shields

A

20 mSv

51
Q

Eye shields reduce dose by ____

A

5-10x

52
Q

How is scatter to clinicians eyes from below front and side limited?

A

wraparound design minimises gaps

comfort

53
Q

Under IRR17 if working with ionising radiation

A

1) employer must consult an RPA
2) ensure there is appropriate notification, registration or consent
3) carry out risk assessment
4) appoint RPS
5) ensure staff are trained and aware of local rules

54
Q

A room should be designed with the aim of _____

A

keeping doses ALARP and ensuring dose limits are not exceeded

55
Q

Room design should consider:

A
  • dose constraints
  • occupancies outside the facility
  • choice of shielding material
  • provision for dismantling and decommissioning
  • ease of cleaning and decontamination
56
Q

Selection of shielding material is dependent on:

A
  • radiation type and energy
  • thickness and weight
  • ability to combine structure/shielding
  • uniformity of material
  • permanence
  • cost
  • optical transparency
57
Q

shielding materials

A

lead sheet
lead glass and acrylic
concrete and concrete blocks
brick
barium plaster
gypsum plasterboard

58
Q

What data about the beam is more appropriate when considering materials?

A

broad beam attenuation data

59
Q

What data is important about shielding materials?

A

density and uniformity

60
Q

Tenth value layer

A

thickness of material which reduces the dose rate to 0.1 of the incident dose rate
it is energy dependent

61
Q

the fraction of the beam transmitted through material x is described by B =

A

B=10^(-x/TVL)

62
Q

for shielding calculations we need to know:

A
  • primary beam and scattered beam dose rates or DAP workload
  • beam directions
  • workload
  • distances to barriers
  • dose constraint
63
Q

Dose constraint

A

upper level of dose to an individual used at the design or planning stag

64
Q

Dose constraint

A

upper level of dose to an individual used at the design or planning stage
dose constraint < dose limit

65
Q

Occupationally exposed workers dose constraint

A

1mSv

66
Q

members of the public when optimising protection from a single source

A

0.3mSv per year
can account for occupancy

67
Q

ACOP designation of a controlled area

A

dose rate over working day > 7.5 µSvhr-1
OR
instantaneous dose rate > 7.5 µSvhr-1 if employees untrained in radiation protection have access to area

68
Q

instantaneous dose rate

A

dose rate averaged over 1 minute

69
Q

sources of radiation (air kerma on barrier)

A
  1. primary beam
  2. scattered beam
  3. leakage radiation (linacs)
70
Q

scatter depends on

A

kV, angle, area of x-ray beam at scattering point

71
Q

Typical dlp for a chest-abdo-pelvic ct scan

A

1000 mGy.cm

72
Q

leakage radiation

A

comes from tube housing - heavily filtered

73
Q

medical and dental guidance notes require leakage to be less than __

A

1m Gy per hour at 1m

74
Q

Why are facilities assessed?

A
  • specified level of protection exists
  • check gaps in shielding (joints, door and window frames, sockets pipes breach walls)
75
Q

How to assess facilities by finding barrier factor

A

use radioactive source/x-ray system
calibrate for distance, thickness of barrier

check for gaps using source/detector or xray/film

76
Q

Site monitoring should be carried out

A

at installations or after modifications
periodic checks
following incidents

77
Q

Duty Holders under IRMER17

A

referrer
practitioner
employer
operator
medical physics expert

78
Q

conditions for exposing people of reproductive potential

A

age range 12-55
exposures irradiating between knees and diaphragm

79
Q

procedures for people of reproductive potential

A

establish pregnancy

if definitely pregnant, rejustify exposure accounting for fetus

if pregnancy cannot be excluded, use a low dose <10mGy

80
Q

where pregnancy cannot be excluded and a high dose is required:

A

treat as pregnant

to avoid carry out procedures within first 10 days after period

81
Q

CSAUE

A

clinically significant accidental unintended exposures under IRMER17

82
Q

accidental exposure

A

person receives an exposure in error when no exposure of any kind was intended

83
Q

accidental exposures are reportable at:

A

1mSv in a child effective dose
3mSv in an adult effective dose

84
Q

unintended exposure

A

where an exposure was intended but person receives an exposure significantly higher or different to intended

85
Q

examples of unintended exposure

A

dose received, wrong modality/technique, wrong anatomy, radiopharmaceutical or timing of exposure

86
Q

unintended exposures are caused by

A

procedures, systematic or human error
equipment malfunction

87
Q

unintended exposures due to equipment malfunction are reported under

A

IRMER

88
Q

“equipment” malfunction in unintended exposures refers to

A

equipment delivering radiation and ancillary equipment influencing dose e.g., contrast injectors, software, PACS and RIS

89
Q

SAUE incidents reported to CQC:

A

notification no later than 2 weeks post incident
final report no later than 12 weeks post incident

Medical Imaging (3 decks)

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