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RAD 400 > Test 1 > Flashcards

Test 1 Flashcards

1
Q

Absorbed dose at depth as a percent of a dose at Dmax on central axis (CA) of the beam; percent of beam that’s left
What percent of dose occurs at certain depth

A

Percent depth dose (PDD)

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2
Q

PDD formula

A

PDD = Dd/Dmax or TD/GD or Rx/max dose

Dd = dose at depth
TD = tumor dose
GD = given dose
Rx = prescription
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3
Q

Max dose occurs at Dmax (electronic equilibrium)

A

Given dose

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4
Q

Doses made at __________ because of flattening filter (lateral horns before ___ cm, forward peaked after ___ cm)

A

Central axis, 10cm

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5
Q

TD formula

A

TD = PDD(GD)

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6
Q

Finding an unknown data point between two known points

A

Interpolation

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7
Q

Increase beam energy = _______ dose at depth, less attenuation/________ PDD

A

Increase

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8
Q

Increase calculation depth (go through more tissue) = ________ PDD because of more tissue attenuation

A

Decrease

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9
Q

Increase field size = _______ time/MUs

A

Decrease

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10
Q

Increase SSD = __________ time

A

Increase

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11
Q

Scatter of a square field to scatter of a rectangular field

A

Equivalent square

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12
Q

What is the advantage of an isocentric technique?

A

Don’t have to set up patient every time

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13
Q

Mayneord factor (MF) formula

A

MF = (((New SSD + Dmax)^2)/((new SSD + depth)^2))/(((old SSD + Dmax)^2)/((old SSD + depth)^2))

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14
Q

New PDD formula

A

New PDD = old PDD x MF

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15
Q

POI

A

Point of interest = TD

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16
Q

Dmax ________ with increasing FS because more scatter and less penetrating beam; increase electron contamination that occurs when the collimator is open wider

A

Decreases

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17
Q

SSD MUs formula

A

MU = GD/(Dfs x PSF)

Dfs = collimator field size
PSF = effective field size
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18
Q

Amount of time it takes to deliver 1 cGy to Dmax for 10x10 FS, 100 cm away

A

Monitor unit (MU)

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19
Q

Dependent on collimator size/scatter

Collimator field size

A 
Dfs
Collimator scatter (Sc)
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20
Q

Increase collimator size = ________ scatter = ________ time to deliver dose

A

Increase, decrease

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21
Q

MUs ______ with increased energy because of more penetrating beam

A

Decrease

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22
Q

Scatter on patient; SSD at surface, SAD at depth
Enhancement in dose going from “free space” to in phantom
Compares primary and total radiation
TAR at Dmax because most scatter occurs at Dmax

A

Peak scatter factor (PSF)

Effective field size

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23
Q

Scatter factor for low energy x-rays

A

Back scatter factor (BSF)

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24
Q

Area that’s coldest because it’s where the beam is attenuated the most

A

Prescription (Rx)

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25
______ of wedge at thinner part of breast; this decreases apical dose and pushes dose to thicker part
Heel
26
Dose highest at ______ (about ___ cm deep) because of buildup and at apex of breast because it's thinner
Surface, 3 cm
27
SSD setup depends on ______, SAD ________
PDD, independent
28
Ratio of dose in air versus dose in tissue after it's been attenuated, more convenient for SAD treatments because it's independent of SSD
Tissue-air ratio (TAR)
29
SAD MU equation
MU = TD/(Dfs x INV^2 x TAR)
30
SAD POI equation
POI = MU x Dfs x INV^2 x TARpoi
31
Output equation
Dfs x INV^2
32
Increase scatter = _______ time; increase energy = _________ time/MU
Decrease
33
Increase PSF = ________ treatment time
Decrease
34
Highest PSF
1.5 for large fields at orthovoltage energies (150-500 kV)
35
Increase SSD = ______ in TAR because they're at same distance
No change
36
Decrease FS = ________ MU
Increase MU (less scatter so machine has to be on longer)
37
2 ways dose is lost
Inverse square law | Attenuation
38
Increase beam energy = _________ PDD/percent transmitted
Increase
39
Increase SSD = __________ PDD
Increase
40
Increase field size = __________ PSF because increasing field size increases scatter
Increase
41
Increase energy = ________ PSF
Decrease
42
Corrects for old and new SSD | Ratio of two PDDs
Mayneord factor (MF)
43
Ratio of the dose at a given point in phantom to the dose at the same point at a fixed reference depth, independent of SSD
Tissue-phantom ratio (TPR)
44
MUs and dose are _________ proportional
Directly
45
Typical breast bridge diameter
20-30 cm
46
Percent hotspot formula
GD/TD
47
Equivalent square formula
4A/P ``` A = area P = perimeter ```
48
Dmax of a Co-60, 4X, 6X, 10X, 15X and 18X beam
``` Co-60 = 0.5 cm 4X = 1 cm 6X = 1.5 cm 10X = 2.5 cm 15 X = 3 cm 18X = 3 cm ```
49
7 things dose distributions vary with (beam characteristics and patient)
``` Beam energy Calculation depth Field size Beam modifiers (wedges, MLCs) Distance from source Patient contour Tissue inhomogeneities (lung, bone, water, etc.) ```
50
2 contributions/components of beam
Primary | Scatter
51
Radiation that comes directly from the source without being scattered and usually contributes most dose
Primary radiation
52
Dose from photons that deposit energy after having undergone one or more scattering events; photons that have only done this once are most prominent Difficult to directly compute to dose
Scatter radiation
53
Scatter ________ with increased volume of material irradiation (large field sizes); more matter is irradiated as field size increases, and therefore more radiation can be scattered to the observation point
Increases
54
Most accurate and best algorithm but takes a lot of computational power
Monte Carlo
55
When field size becomes very large, radiation scattered from central axis will be attenuated before it can reach central axis; in this case a further increase in field size will result in a __________ increase in dose
Negligible
56
Homogenous phantom that is tissue equivalent
Water
57
Dose hits surface and begins to rise to reach Dmax
Buildup region
58
Depth where dose reaches maximum value; scatter in equal to scatter out
Dmax | Electronic equilibrium
59
Radiation begins to attenuate and decrease as depth increases
Fall-off
60
Distance of DDs added to distance from source
Dose at depth (Dd)
61
Increase field size = _________ PDD because there's more volume irradiated which contributes more scatter to the measurement point on central axis
Increase

RAD 400 (4 decks)

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