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FRCR Part 1 Physics > Patient Dosimetry (Erin) > Flashcards

Patient Dosimetry (Erin) Flashcards

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1
Q

In Xray:
Does a higher tube current (mA) increase or decrease patient dose?

A

Increases patient dose

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2
Q

In Xray:
Does a longer exposure time (s) increase or decrease patient dose?

A

Increases patient dose

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3
Q

In Xray:
Does a wider collimation increase or decrease patient dose?

A

Increase patient dose (reduces scatter and irradiated area)

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4
Q

In Xray:
Dose a smaller FOV increase or decrease patient dose?

A

Decreases

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5
Q

In Xray:
does a higher kVP increase or decrease patient dose?

A

Increases patient doseA

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6
Q

List the 4 beam properties that increase patient dose in xray?

A

Higher mA
higher kVp
Larger FOV
Wider collimation

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7
Q

In Xray:
Dose a larger FOV increase or decrease patient dose?

A

Increases

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8
Q

In Xray:
Does a lower tube current (mA) increase or decrease patient dose?

A

Decreases

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9
Q

In Xray:
Does a shorter exposure time (s) increase or decrease patient dose?

A

Decreases

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10
Q

In Xray:
Does filtration increase or decrease patient dose?

A

Decreases

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11
Q

In Xray:
Does the use of a grid increase or decrease patient dose?

A

Increases

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12
Q

In Xray:
Does reduced receptor sensitivity increase or decrease patient dose?

A

IncreasesN

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13
Q

List the 3 scanner properties that increase patient dose in Xray

A

No filtration
Use of a grid
Reduced receptor sensitivity

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14
Q

In Xray:
Does NO filtration increase or decrease patient dose?

A

Increases

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15
Q

In Xray:
Does a lack of grid increase or decrease patient dose?

A

Decreases

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16
Q

In Xray:
Does increased receptor sensitivity increase or decrease patient dose?

A

Decreases

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17
Q

List the 2 patient properties which increase patient dose in xray imaging

A

Closer to focal spot (xray source)
Larger patient habitus (larger skin surface to absorb maximum dose)

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18
Q

Does moving the patient further from the focal spot increase or decrease patient dose in xray?

A

Decreases

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19
Q

In Xray:
Does moving the patient closer to focal spot increase or decrease patient dose?

A

Increases

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20
Q

In fluoroscopy:
Does a lower kVp increase or decrease patient dose?

A

Increases (a less penetrating beam means more radiation absorbed particularly on the skin)

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21
Q

In fluoroscopy:
Does continuous or pulsed technique give a higher patient does?

A

Continuous

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22
Q

In fluoroscopy:
Does a larger area of collimation increase or decrease patient dose?

A

Increases

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23
Q

In fluoroscopy:
Does a smaller area of collimation increase or decrease patient dose?

A

Decreases

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24
Q

In fluoroscopy:
Does the use of a grid increase or decrease patient dose?

A

Increase

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25
Q

In fluoroscopy:
Does NO grid increase or decrease patient dose?

A

Decrease

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26
Q

In fluoroscopy:
Does increase electrical magnification (zoom modes) increase or decrease patient dose?

A

Increase

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27
Q

In fluoroscopy:
Does increased geometric magnification (moving patient closer to the source) increase or decrease patient dose?

A

Increase

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28
Q

In fluoroscopy:
Does an obese patient receive increased or decreased dose?

A

Increased

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29
Q

List the 3 scanner properties that increase dose in fluoroscopy

A
  1. Use of a grid
  2. Increased electrical magnification (zoom mode)
  3. Increased geometric magnification (i.e moving patient closer to the source, or detector closer to source)
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30
Q

In CT:
Does higher mA increase or decrease patient dose?

A

Increases

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31
Q

In CT:
Does lower mA increase or decrease patient dose?

A

Decreases

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32
Q

In CT:
Does higher kV increase or decrease patient dose?

A

Increases

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33
Q

In CT:
Does lower kV increase or decrease patient dose?

A

Decreases

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34
Q

In CT:
Does longer exposure time increase or decrease patient dose?

A

Increase

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35
Q

In CT:
Does shorter exposure time increase or decrease patient dose?

A

Decrease

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36
Q

In CT:
Does NOT using mA modulation increase or decrease patient dose?

A

Increases

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37
Q

In CT:
Does using mA modulation increase or decrease patient dose?

A

Decrease

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38
Q

In CT:
Does wider collimation increase or decrease patient dose?

A

Increases
However if collimation is too small the system will compensate by increasing mA/kVp

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39
Q

In CT:
Does decreasing pitch increase or decrease patient dose?

A

Increases

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40
Q

In CT:
Does increasing pitch increase or decrease patient dose?

A

Decreases

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41
Q

In CT:
Does a smaller patient receive increases or decreased dose?

A

Increased
More xrays will penetrate to the centre and deposit a higher dose
NB a larger patient will receive more total xrays but dose is measured per unit mass

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42
Q

In Nuclear Imaging:
Does an increased amount of injected activity increase or decrease patient dose?

A

Increases

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43
Q

In Nuclear Imaging:
Does an decreased amount of injected activity increase or decrease patient dose?

A

Decreases

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44
Q

In Nuclear Imaging:
What is the result of reduced patient drinking/urination on patient dose?

A

Increased patient dose (slower loss of activity from bladder)

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45
Q

In Nuclear Imaging:
What is the result of increased patient drinking/urination on patient dose?

A

Decreased patient dose

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46
Q

What is the effective dose of a cardiac CT?

A

12mSv

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47
Q

What is the effective dose of a CT abdomen pelvis

A

10mSv

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48
Q

What is the effective dose of a CT head?

A

2mSv

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49
Q

LAC equation?

A

μLAC = 0.693* / HVL

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50
Q

MAC equation?

A

μMAC = μLAC/ρ

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51
Q

To calculate the intensity of a beam (I) of x-ray photons after they have passed through a filter…(equation)

A

I = Io e-μd

e = energy
u = LAC
d = thickness of filter

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52
Q

Describe how radiation can directly affect biological molecules

A

Atoms within the DNA molecule are directly ionised by radiation leading to molecular damage
Breaking atomic bonds or causing base alteration

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53
Q

Describe how radiation can indirectly affect biological molecules

A

Water molecules interact with radiation to create free radicals which then migrate to the DNA molecule and cause molecular damage (breaking atomic bonds or causing base alteration)

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54
Q

How is absorbed dose (D) measured (formula)

A

D = E/m
E = energy deposited in a medium
M = mass of medium

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55
Q

What unit is absorbed dose measured in

A

Gray (Gy)

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56
Q

What is 1Gy equal to in J/kg

A

1Gy = 1J/kg

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57
Q

What is 1Gy in mGy

A

1Gy = 1000mGy (milligray)

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58
Q

What is 1mGy in uGy

A

1mGy = 1000 uGy (microgray)

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59
Q

What is the radiation weighting factor of X-rays and gamma photons

A

1

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60
Q

What is the radiation weighting factors of electrons and/positrons

A

1

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61
Q

What is the weighting factor of alpha particles

A

20

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62
Q

How is equivalent dose calculated

A

D (absorbed dose) x Radiation weighting factor

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63
Q

Do alpha particles have a high or low LET

A

High LET

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64
Q

Do beta particles have a high or low LET

A

Low LET

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65
Q

What units is equivalent dose measured in

A

Sv
(1Sv = 1000mSv)

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66
Q

How is effective dose calculated

A

Sum of (Equivalent dose x tissue weighting factor)

67
Q

What is the tissue weighting factor for bone marrow, breast, colon, lungs and stomach

A

0.12

68
Q

What is the tissue weighting factor for the gonads

A

0.08

69
Q

What is the tissue weighting factor for the bladder, liver, oesophagus and thyroid

A

0.04

70
Q

What is the tissue weighting factor for brain, bone surfaces skin and salivary glands

A

0.01

71
Q

Rank in order from most tissue sensitive to least tissue sensitivity
Gonads
Salivary glands
Liver
Bone marrow

A

Most Sensitive

  • Bone marrow
  • Gonads
  • Liver
  • Salivary Glands

Least sensitive

72
Q

What are the 3 damage effects can radiation have on DNA

A

No biological effect (tissue repaired)
Cell death
Cell mutation

73
Q

What are some examples of deterministic effects

A

Cataract formation
Skin erythema/necrosis/ulceration
Bone marrow suppression
Sterility (can be temporary or permanent depending on dose)
Death

74
Q

When do deterministic effects typically occur

A

Soon after exposure

75
Q

What are deterministic effects due to

A

Cell death

76
Q

How does the severity of deterministic effects change with increasing dose

A

Severity of deterministic effects increase with increasing dose (above a certain threshold)

77
Q

How does the probability of stochastic effects change with increasing dose

A

Probability of stochastic effects increases with increasing dose

78
Q

What does ALARP stand for

A

As low as reasonably practicable

79
Q

When do stochastic effects typically occur

A

Many years after exposure

80
Q

What is the main stochastic effect we are concerned about

A

Cancer

81
Q

What is the cancer risk for exposure to 1mSv

A

1 in 20,000 for 1mSv exposure

82
Q

What is the Gy threshold for skin necrosis

A

10Gy

83
Q

What is the Gy threshold for cataract formation

A

0.5Gy

84
Q

What is the Gy threshold for bone marrow suppression

A

0.5Gy

85
Q

What is the Gy threshold for skin erythema

A

2Gy

86
Q

What is the Gy threshold for Testes - temporary sterility

A

0.15 Gy

87
Q

What is the threshold for stochastic effects

A

NO THRESHOLD

88
Q

What is the excess childhood cancer risk per 1mSv of exposure

A

1 in 13,000 per mSv

89
Q

What is the natural risk of paediatric cancer

A

1 in 500

90
Q

What foetal dose (in mSv) will double the natural risk of paediatric cancer

A

25 mSv

91
Q

What is the typical effective dose of an extremity xray

A

<0.01 mSv

92
Q

What is the typical effective dose of chest xray

A

0.1 mSv

93
Q

What is the typical effective dose of a lumbar spine xray

A

1.3 mSv

94
Q

What is the typical effective dose of barium enema

A

7 mSv

95
Q

What is the typical effective dose of CT head

A

2 mSv

96
Q

What is the typical effective dose of a CTAP

A

10 mSv

97
Q

What is the typical effective dose of a CT Chest

A

8 mSv

98
Q

What is the typical effective dose of a bone scan (NM)

A

4 mSv

99
Q

What is the typical effective dose of PDG PET Scan

A

8 mSv

100
Q

What is the typical effective dose of a lung perfusion scan (NM)

A

1 mSv

101
Q

For a point source what law does the dose rate follow

A

Inverse square law

102
Q

What is the inverse square law equation

A

1/d(squared)

103
Q

Doubling your distance from an xray source decreases your dose by a factor of ………

A

4

104
Q

How much protection do lead aprons provide from the primary xray beam

A

NONE
They protect against scattered radiation but not the primary beam

105
Q

What materials are commonly used for radiation shielding

A

Lead and tungsten

106
Q

What crystals are TLD made from

A

Lithium fluoride
Or
Calcium fluoride

107
Q

Why is lithium fluoride used for TLD

A

Because has a similar atomic number to soft tissue

108
Q

How do TLD work?

A

Small crystals which absorb ionising radiation and emit light when exposed to heat

109
Q

Can TLD be reused

A

Yes
Usually worn for 1-2 months then sent away for processing
Then reused

110
Q

How many TLDs does a body dosimeter comprise of?

A

2

111
Q

What are the functions of the 2 TLDs in a body dosimeter

A

One TLD measures skin dose
The other TLD measures dose at a depth of 1cm

112
Q

What does KERMA stand for

A

Kinetic energy released to matter

113
Q

What is KERMA very similar to

A

Absorbed dose (especially at lower energies)

114
Q

What piece of equipment allows air kerma to be measures

A

Ionisation chamber

115
Q

Is the dose area product linked to stochastic or deterministic risk

A

Stochastic

116
Q

What is the typical exposure from a long haul flight

A

0.08mSv

117
Q

What is the largest source of background radiation

A

Exposure to radon

118
Q

With a lead thickness of 0.25mm what % of photons are transmitted

A

5%

119
Q

With a lead thickness of 0.35mm what % of photons are transmitted

A

3%

120
Q

With a lead thickness of 0.5mm What % of photons are transmitted

A

1.5%

121
Q

What particles does radon gas produce

A

Alpha particles

122
Q

What unit is Kerma measured in

A

J/kg-1

123
Q

if someone is a classified worker how long must their dose records be kept for

A

Minimum 30 years

124
Q

For how long do classified workers need dose records kept?
How often do they need a medical exam?
How old do they have to be?

A

Must be >18yrs
Have their dose records kept for minimum of 30 years
Undergo a medical examination before they are classified then annually thereafter

125
Q

All procedures must have a DAP or dose administered recorded T or F

A

True

126
Q

How is the DRL decided

A

Every procedure must have a DAP or dose administered recorded
From all these recordings a local DRL is set as the third quartile of the median dose
National DRL set as the third quartile of all the relevant local DRL

127
Q

Can TLD differentiate between the type of radiation you are exposed to?

A

No

128
Q

Can TLD measure dose rate?

A

No

129
Q

Can TLD be used to measure eye doses?

A

Yes as they can be made into various shapes, they can be used for assessment of example eye or finger doses

130
Q

Can TLD be reused?

A

Yes

131
Q

Can TLD be used to measure superficial and deep doses?

A

Yes

132
Q

Are film dosimetry badges able to differentiate between the different types of radiation exposure?

A

Yes

133
Q

Can film badges differentiated between the different energies of photons?

A

Yes

134
Q

What are film badges made from

A

Silver halide

135
Q

Advantages of film badges

A
  • Cheap
  • Can distinguish between different energies of photons
  • Can measure doses from different types of radiation
  • Provide a permanent record
    C- Accurate for exposures > 100 millirem
136
Q

Can film badges be reused?

A

No

137
Q

Which are more expensive TLD or film badges?

A

TLD

138
Q

Can TLD store dose records?

A

No once information is read out it is lost

139
Q

Are TLD or film badges more sensitivty

A

Relatively similar

140
Q

Can TLD provide a direct reading of dose

A

No

141
Q

Can TLD provide a permanent record of dose?

A

No

142
Q

Can TLD measure radioactive contamination?

A

No

143
Q

How many times can the dose of a TLD be read?

A

Once

144
Q

Are TLD affected by environmental factors?

A

Yes

145
Q

What is the sensitivity of film badges in mSv

A

0.1-0.2mSv

146
Q

Can film badges be used to measure finger dose

A

No
TLD

147
Q

Do film badges provide permanent record of exposure

A

Yes

148
Q

How often are film badges usually replaced?

A

1 month
Due to fogging

149
Q

Do film badges measure the effective dose T/F?

A

False
Measure absorbed dose

150
Q

What are the most commonly used detectors in electronic dosimeters?

A

Silicone diode detector

151
Q

What is the most sensitive type of dosimeter

A

Electronic dosimeters
Sensitive to the nearest 1uSv

152
Q

What is a drawback to electronic dosimeters

A

Expensive

153
Q

How many more times sensitive are electronic dosimeters compared to TLD

A

100 times

154
Q

Benefits of electronic dosimeters

A
  • Can provide direct electronic readout
    -Can provide live/real time readouts
  • Don’t need processing like TLD
155
Q

Can electronic dosimeters measure dose and dose rates

A

Yes

156
Q

Do electronic dosimeters provide a direct reading

A

Yes

157
Q

Are electronic dosimeters good for measuring pregnancy dose

A

Yes

158
Q

What is the effective dose for an AXR

A

0.7mSv

159
Q

What is the effective dose for a dental xray

A

0.004/0.005mSv

160
Q

What is the effective dose of a barium swallow

A

0.2mSv

161
Q
A
162
Q

Air kerma rate (mGy/s) can be measured using…?

A

An ionisation chamber, at a known distance from the X-ray tube

163
Q

In CT: what is beam modulation?

A

A method of reducing the dose by altering the mA dynamically, depending on what part of the body you’re at (done automatically by a computer)

FRCR Part 1 Physics (20 decks)

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