Patient Dosimetry (Erin) Flashcards
1
Q
In Xray:
Does a higher tube current (mA) increase or decrease patient dose?
A
Increases patient dose
2
Q
In Xray:
Does a longer exposure time (s) increase or decrease patient dose?
A
Increases patient dose
3
Q
In Xray:
Does a wider collimation increase or decrease patient dose?
A
Increase patient dose (reduces scatter and irradiated area)
4
Q
In Xray:
Dose a smaller FOV increase or decrease patient dose?
A
Decreases
5
Q
In Xray:
does a higher kVP increase or decrease patient dose?
A
Increases patient doseA
6
Q
List the 4 beam properties that increase patient dose in xray?
A
Higher mA
higher kVp
Larger FOV
Wider collimation
7
Q
In Xray:
Dose a larger FOV increase or decrease patient dose?
A
Increases
8
Q
In Xray:
Does a lower tube current (mA) increase or decrease patient dose?
A
Decreases
9
Q
In Xray:
Does a shorter exposure time (s) increase or decrease patient dose?
A
Decreases
10
Q
In Xray:
Does filtration increase or decrease patient dose?
A
Decreases
11
Q
In Xray:
Does the use of a grid increase or decrease patient dose?
A
Increases
12
Q
In Xray:
Does reduced receptor sensitivity increase or decrease patient dose?
A
IncreasesN
13
Q
List the 3 scanner properties that increase patient dose in Xray
A
No filtration
Use of a grid
Reduced receptor sensitivity
14
Q
In Xray:
Does NO filtration increase or decrease patient dose?
A
Increases
15
Q
In Xray:
Does a lack of grid increase or decrease patient dose?
A
Decreases
16
Q
In Xray:
Does increased receptor sensitivity increase or decrease patient dose?
A
Decreases
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)
18
Q
Does moving the patient further from the focal spot increase or decrease patient dose in xray?
A
Decreases
19
Q
In Xray:
Does moving the patient closer to focal spot increase or decrease patient dose?
A
Increases
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)
21
Q
In fluoroscopy:
Does continuous or pulsed technique give a higher patient does?
A
Continuous
22
Q
In fluoroscopy:
Does a larger area of collimation increase or decrease patient dose?
A
Increases
23
Q
In fluoroscopy:
Does a smaller area of collimation increase or decrease patient dose?
A
Decreases
24
Q
In fluoroscopy:
Does the use of a grid increase or decrease patient dose?
A
Increase
25
In fluoroscopy:
Does NO grid increase or decrease patient dose?
Decrease
26
In fluoroscopy:
Does increase electrical magnification (zoom modes) increase or decrease patient dose?
Increase
27
In fluoroscopy:
Does increased geometric magnification (moving patient closer to the source) increase or decrease patient dose?
Increase
28
In fluoroscopy:
Does an obese patient receive increased or decreased dose?
Increased
29
List the 3 scanner properties that increase dose in fluoroscopy
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)
30
In CT:
Does higher mA increase or decrease patient dose?
Increases
31
In CT:
Does lower mA increase or decrease patient dose?
Decreases
32
In CT:
Does higher kV increase or decrease patient dose?
Increases
33
In CT:
Does lower kV increase or decrease patient dose?
Decreases
34
In CT:
Does longer exposure time increase or decrease patient dose?
Increase
35
In CT:
Does shorter exposure time increase or decrease patient dose?
Decrease
36
In CT:
Does NOT using mA modulation increase or decrease patient dose?
Increases
37
In CT:
Does using mA modulation increase or decrease patient dose?
Decrease
38
In CT:
Does wider collimation increase or decrease patient dose?
Increases
However if collimation is too small the system will compensate by increasing mA/kVp
39
In CT:
Does decreasing pitch increase or decrease patient dose?
Increases
40
In CT:
Does increasing pitch increase or decrease patient dose?
Decreases
41
In CT:
Does a smaller patient receive increases or decreased dose?
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
42
In Nuclear Imaging:
Does an increased amount of injected activity increase or decrease patient dose?
Increases
43
In Nuclear Imaging:
Does an decreased amount of injected activity increase or decrease patient dose?
Decreases
44
In Nuclear Imaging:
What is the result of reduced patient drinking/urination on patient dose?
Increased patient dose (slower loss of activity from bladder)
45
In Nuclear Imaging:
What is the result of increased patient drinking/urination on patient dose?
Decreased patient dose
46
What is the effective dose of a cardiac CT?
12mSv
47
What is the effective dose of a CT abdomen pelvis
10mSv
48
What is the effective dose of a CT head?
2mSv
49
LAC equation?
μLAC = 0.693* / HVL
50
MAC equation?
μMAC = μLAC/ρ
51
To calculate the intensity of a beam (I) of x-ray photons after they have passed through a filter...(equation)
I = Io e-μd
e = energy
u = LAC
d = thickness of filter
52
Describe how radiation can directly affect biological molecules
Atoms within the DNA molecule are directly ionised by radiation leading to molecular damage
Breaking atomic bonds or causing base alteration
53
Describe how radiation can indirectly affect biological molecules
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)
54
How is absorbed dose (D) measured (formula)
D = E/m
E = energy deposited in a medium
M = mass of medium
55
What unit is absorbed dose measured in
Gray (Gy)
56
What is 1Gy equal to in J/kg
1Gy = 1J/kg
57
What is 1Gy in mGy
1Gy = 1000mGy (milligray)
58
What is 1mGy in uGy
1mGy = 1000 uGy (microgray)
59
What is the radiation weighting factor of X-rays and gamma photons
1
60
What is the radiation weighting factors of electrons and/positrons
1
61
What is the weighting factor of alpha particles
20
62
How is equivalent dose calculated
D (absorbed dose) x Radiation weighting factor
63
Do alpha particles have a high or low LET
High LET
64
Do beta particles have a high or low LET
Low LET
65
What units is equivalent dose measured in
Sv
(1Sv = 1000mSv)
66
How is effective dose calculated
Sum of (Equivalent dose x tissue weighting factor)
67
What is the tissue weighting factor for bone marrow, breast, colon, lungs and stomach
0.12
68
What is the tissue weighting factor for the gonads
0.08
69
What is the tissue weighting factor for the bladder, liver, oesophagus and thyroid
0.04
70
What is the tissue weighting factor for brain, bone surfaces skin and salivary glands
0.01
71
Rank in order from most tissue sensitive to least tissue sensitivity
Gonads
Salivary glands
Liver
Bone marrow
Most Sensitive
- Bone marrow
- Gonads
- Liver
- Salivary Glands
Least sensitive
72
What are the 3 damage effects can radiation have on DNA
No biological effect (tissue repaired)
Cell death
Cell mutation
73
What are some examples of deterministic effects
Cataract formation
Skin erythema/necrosis/ulceration
Bone marrow suppression
Sterility (can be temporary or permanent depending on dose)
Death
74
When do deterministic effects typically occur
Soon after exposure
75
What are deterministic effects due to
Cell death
76
How does the severity of deterministic effects change with increasing dose
Severity of deterministic effects increase with increasing dose (above a certain threshold)
77
How does the probability of stochastic effects change with increasing dose
Probability of stochastic effects increases with increasing dose
78
What does ALARP stand for
As low as reasonably practicable
79
When do stochastic effects typically occur
Many years after exposure
80
What is the main stochastic effect we are concerned about
Cancer
81
What is the cancer risk for exposure to 1mSv
1 in 20,000 for 1mSv exposure
82
What is the Gy threshold for skin necrosis
10Gy
83
What is the Gy threshold for cataract formation
0.5Gy
84
What is the Gy threshold for bone marrow suppression
0.5Gy
85
What is the Gy threshold for skin erythema
2Gy
86
What is the Gy threshold for Testes - temporary sterility
0.15 Gy
87
What is the threshold for stochastic effects
NO THRESHOLD
88
What is the excess childhood cancer risk per 1mSv of exposure
1 in 13,000 per mSv
89
What is the natural risk of paediatric cancer
1 in 500
90
What foetal dose (in mSv) will double the natural risk of paediatric cancer
25 mSv
91
What is the typical effective dose of an extremity xray
<0.01 mSv
92
What is the typical effective dose of chest xray
0.1 mSv
93
What is the typical effective dose of a lumbar spine xray
1.3 mSv
94
What is the typical effective dose of barium enema
7 mSv
95
What is the typical effective dose of CT head
2 mSv
96
What is the typical effective dose of a CTAP
10 mSv
97
What is the typical effective dose of a CT Chest
8 mSv
98
What is the typical effective dose of a bone scan (NM)
4 mSv
99
What is the typical effective dose of PDG PET Scan
8 mSv
100
What is the typical effective dose of a lung perfusion scan (NM)
1 mSv
101
For a point source what law does the dose rate follow
Inverse square law
102
What is the inverse square law equation
1/d(squared)
103
Doubling your distance from an xray source decreases your dose by a factor of .........
4
104
How much protection do lead aprons provide from the primary xray beam
NONE
They protect against scattered radiation but not the primary beam
105
What materials are commonly used for radiation shielding
Lead and tungsten
106
What crystals are TLD made from
Lithium fluoride
Or
Calcium fluoride
107
Why is lithium fluoride used for TLD
Because has a similar atomic number to soft tissue
108
How do TLD work?
Small crystals which absorb ionising radiation and emit light when exposed to heat
109
Can TLD be reused
Yes
Usually worn for 1-2 months then sent away for processing
Then reused
110
How many TLDs does a body dosimeter comprise of?
2
111
What are the functions of the 2 TLDs in a body dosimeter
One TLD measures skin dose
The other TLD measures dose at a depth of 1cm
112
What does KERMA stand for
Kinetic energy released to matter
113
What is KERMA very similar to
Absorbed dose (especially at lower energies)
114
What piece of equipment allows air kerma to be measures
Ionisation chamber
115
Is the dose area product linked to stochastic or deterministic risk
Stochastic
116
What is the typical exposure from a long haul flight
0.08mSv
117
What is the largest source of background radiation
Exposure to radon
118
With a lead thickness of 0.25mm what % of photons are transmitted
5%
119
With a lead thickness of 0.35mm what % of photons are transmitted
3%
120
With a lead thickness of 0.5mm What % of photons are transmitted
1.5%
121
What particles does radon gas produce
Alpha particles
122
What unit is Kerma measured in
J/kg-1
123
if someone is a classified worker how long must their dose records be kept for
Minimum 30 years
124
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?
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
All procedures must have a DAP or dose administered recorded T or F
True
126
How is the DRL decided
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
Can TLD differentiate between the type of radiation you are exposed to?
No
128
Can TLD measure dose rate?
No
129
Can TLD be used to measure eye doses?
Yes as they can be made into various shapes, they can be used for assessment of example eye or finger doses
130
Can TLD be reused?
Yes
131
Can TLD be used to measure superficial and deep doses?
Yes
132
Are film dosimetry badges able to differentiate between the different types of radiation exposure?
Yes
133
Can film badges differentiated between the different energies of photons?
Yes
134
What are film badges made from
Silver halide
135
Advantages of film badges
- 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
Can film badges be reused?
No
137
Which are more expensive TLD or film badges?
TLD
138
Can TLD store dose records?
No once information is read out it is lost
139
Are TLD or film badges more sensitivty
Relatively similar
140
Can TLD provide a direct reading of dose
No
141
Can TLD provide a permanent record of dose?
No
142
Can TLD measure radioactive contamination?
No
143
How many times can the dose of a TLD be read?
Once
144
Are TLD affected by environmental factors?
Yes
145
What is the sensitivity of film badges in mSv
0.1-0.2mSv
146
Can film badges be used to measure finger dose
No
TLD
147
Do film badges provide permanent record of exposure
Yes
148
How often are film badges usually replaced?
1 month
Due to fogging
149
Do film badges measure the effective dose T/F?
False
Measure absorbed dose
150
What are the most commonly used detectors in electronic dosimeters?
Silicone diode detector
151
What is the most sensitive type of dosimeter
Electronic dosimeters
Sensitive to the nearest 1uSv
152
What is a drawback to electronic dosimeters
Expensive
153
How many more times sensitive are electronic dosimeters compared to TLD
100 times
154
Benefits of electronic dosimeters
- Can provide direct electronic readout
-Can provide live/real time readouts
- Don't need processing like TLD
155
Can electronic dosimeters measure dose and dose rates
Yes
156
Do electronic dosimeters provide a direct reading
Yes
157
Are electronic dosimeters good for measuring pregnancy dose
Yes
158
What is the effective dose for an AXR
0.7mSv
159
What is the effective dose for a dental xray
0.004/0.005mSv
160
What is the effective dose of a barium swallow
0.2mSv
161
162
Air kerma rate (mGy/s) can be measured using…?
An ionisation chamber, at a known distance from the X-ray tube
163
In CT: what is beam modulation?
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)
