Midterm Exam Flashcards
1
Q
What is Roentgen?
A
Unit of exposure in air
2
Q
What is a Rad?
A
Radiation Absorbed Dose
3
Q
What is an f factor?
A
Roentgen to cGy conversion factor
4
Q
What factors affect the f factor?
A
Machine Energy and Density of Material
5
Q
1 Rad =
A
1 cGy
6
Q
1 Roentgen (R) =
A
2.58 x 10^-4 Coulombs/kilogram of air
7
Q
D/max
A
Depth of maximum absorbed dose and ionization
8
Q
What is the Dmax of a 6 Mv beam?
A
1.5 cm below the skin
9
Q
What is the Dmax of a Co-60 beam?
A
0.5 cm below the skin
10
Q
What is the Dmax of a 10 Mv beam?
A
2.5 cm below the skin
11
Q
What is the Dmax of a 18 Mv beam?
A
3.5 below the skin
12
Q
What is the Dmax of a Orthovoltage machine?
A
On the surface of the skin
13
Q
What affects Dmax? Explain how.
A
Beam Energy, as your increase in beam energy then Dmax goes deeper in the patient
14
Q
What is a Half Value Layer?
A
Some thickness of a material that decrease the beam intensity by half its value
15
Q
How much of the beam remains after 1 HVL?
A
50%
16
Q
How much of the beam remains after 2 HVL?
A
25%
17
Q
How much of the beam remains after 3 HVL?
A
12.5%
18
Q
How much of the beam remains after 4 HVL?
A
6.25%
19
Q
What is the Isocenter?
A
A point of intersection of the collimator axis and gantry axis rotation
20
Q
What is erythema?
A
Skin reddening
21
Q
What is an Erythema dose?
A
The dose amount, which when given with cause skin reddening
22
Q
What is bolus?
A
tissue equivalent material utilized during treatments to raise the dose higher on the skin
23
Q
What is the requirement to be considered bolus?
A
have the same density as tissue
24
Q
What are the 5 common materials utilized as bolus?
A
Rice, Superflab, Water, superstuff, Wax
25
What is SSD?
Source to Skin distance
26
What is SAD? Explain its relationship to SSD.
Source to Axis Distance. SAD is the distance that includes the SSD and Depth of isocenter.
27
What is the simple equation involving SSD used to find SAD?
SSD + Depth = SAD
28
What are the 6 machine types? (Remember mnemonic)
Grenz, Contact, Superficial, Orthovoltage, Supervoltage, Megavoltage
29
What is the range of voltage for Grenz Ray Therapy?
Greater than or equal to 10-15 KvP
30
What is the range of voltage for Contact Therapy?
40-50 KvP
31
What is the range of voltage for Superficial Therapy?
50-150 KvP
32
What is the range of voltage for Orthovoltage Therapy?
150-500 KvP
33
What is the range of voltage for Supervoltage Therapy?
500-1000 KvP
34
What is the range of voltage for Megavoltage Therapy?
Greater than 1 Mv
35
What machines have their Dmax on the Skin?
All except for Megavoltage, Mv is beneath the patients skin.
36
What is the name of the orthovoltage filter and what are the elements in the correct order from patient to end of the filter?
Thoreaus Filter, Aluminum, Copper and Tin
37
Which machines measure their HVL in Aluminum?
Grenz, Contact, and Superficial
38
Which machines measure their HVL in Copper?
Orthovoltage
39
Which machines measure their HVL in Lead?
Megavoltage
40
When is the Grenz ray beam almost fully absorbed?
2mm
41
When is the Contact ray beam almost fully absorbed?
2 cm
42
At what distance is the orthovoltage beam 90%?
2 cm
43
What depth of tumors is superficial therapy common use for?
no greater than 5 mm
44
What are some examples of Megavoltage machines?
Linac, Co-60, Cyclotron, Betatron,
45
What is Inverse Square Law?
Law that supports the intensity of a beam is inversely proportional to the square of the distance`
46
What is Divergence?
As beam travel, they begin to spread out or "Diverge"
47
Whats is the relation behind Divergence?
Directly Proportional
48
What is the inverse square law formula used to calculate?
the intensity of the beam
49
What is the divergence formula used to calculate?
the size of the radiation field
50
What is an equivalent square?
a method of finding an approximate equivalent field size size
51
What is Back Scatter Factor?
Amount of radiation scattered "back" adding to the skin dose, its a ratio of dose with a scattering medium to dose at the same distance from the radiation without a scattering medium
52
What is the other name for Back Scatter factor for Linacs?
Peak Scatter Factor
53
What is the relation between Back Scatter Factor and Tissue Air Ratio (TAR?
Back Scatter factor is equivalent to the TAR at Dmax
54
What is BSF affected by?
Beam Energy, Field size,
55
As Beam energy increases, what happens to BSF?
Decreases
56
As Field Size increases, what happens to BSF?
Increase
57
What is BSF NOT affected by?
SSD
58
How do you calculate BSF at a different distance?
Use the inverse square to calculate the change in dose,
59
What is Percent Depth Dose or PDD?
The ratio of dose at depth compared to the depth at Dmax
60
What is the PDD for any field size, SDD or Beam energy at Dmax?
100%
61
What factors affect PDD?
Beam Energy, Field Size, SSD, Treatment Depth
62
What happens to PDD, when SSD increases?
PDD Increases
63
What happens to PDD, when Beam Energy decreases?
PDD decreases (Less Penetration)
64
What happens to PDD, when Field Size increases?
PDD increase (More Scatter)
65
What happens to PDD, when treatment depth increases?
PDD Increases (Going deeper into patient)
66
What is Mayneord's F Factor?
the formula used to adjust the PDD when there is a change in the SSD. ITS AN APPLICATION OF INVERSE SQUARE LAW
67
What is an application of Inverse Square Law?
Mayneord's F Factor
68
Where should Machine output be measured for PDD MU calculations?
Treatment SSD + D/max
69
Where is the field size measured at for PDD MU calculations?
On the skin
70
What does Sp stand for?
Phantom/Patient scatter
71
What does Sc stand for?
Collimator Scatter
72
What happens to Output factors when the field size is greater than 10x10?
Factor increases (More Scatter)
73
What happens to Output factors when the field size is less than 10x10?
Factor Decreases (Less Scatter)
74
What are some other names for Total dose at Dmax?
Applied Dose, Given Dose, Incident Dose
75
How is Low Energy machine's output calculated?
Low energy machine utilize time in mins and seconds
76
How is High Energy machine's output calculated?
Using Monitor Units
77
What is a monitor unit?
A unit of output measure
78
What is machine output?
dose from a machine, can be measured in air or in phantom using reference field and known distance.
79
What is the common reference field size used?
10x10
80
What is the common reference output used for Linacs?
1.0 cGy/MU
81
What is output factor?
a factor that account for a change in scatter when the field size is different than reference field size.
82
What is described as the ratio of dose of a given field size to dose of the reference field size?
Output factor
83
What is the total D/max dose?
Entrance dose + Exit dose
84
What is Tissue Air Ratio (TAR)?
Ratio of absorbed dose in a given depth to the absorbed dose at the same distance in air.
85
Who developed TAR?
Johns for use in rotational therapy
86
What does equally weighted fields mean?
same dose from each field (Ex: 100 cGy tx, with 2 Equally weighted fields = 2x 50 cGy fields)
87
What does unequal weighted fields mean?
Different doses from each field (Ex: 100 cGy tx, with 2 UNequally weighted fields = 1 x 60 cGy field + 1 x 40 cGy field)
88
What is the simple equation for TAR?
Dose (tissue) / Dose (air)
89
What factors affect TAR?
Beam Energy, Field Size, Treatment Depth
90
What factors DO NOT affect TAR?
SSD
91
As Beam energy increases, what happens to TAR?
Increases
92
As field size increases, what happens to TAR?
Increases
93
As Treatment depth increases, what happens to TAR?
decrease (deeper into patient)
94
For TAR MU calculations, where should machine output be measured?
Treatment SAD
95
For TAR MU calculations, where should field size be measured?
Treatment SAD
96
What is any treatment less than 360 degrees?
Arc
97
What is any treatment that is 360 degrees?
Rotational
98
Why is Sc only used in the TAR MU calculations?
Sp is built into the TAR table
