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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
Q

______ of wedge at thinner part of breast; this decreases apical dose and pushes dose to thicker part

A

Heel

26
Q

Dose highest at ______ (about ___ cm deep) because of buildup and at apex of breast because it’s thinner

A

Surface, 3 cm

27
Q

SSD setup depends on ______, SAD ________

A

PDD, independent

28
Q

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

A

Tissue-air ratio (TAR)

29
Q

SAD MU equation

A

MU = TD/(Dfs x INV^2 x TAR)

30
Q

SAD POI equation

A

POI = MU x Dfs x INV^2 x TARpoi

31
Q

Output equation

A

Dfs x INV^2

32
Q

Increase scatter = _______ time; increase energy = _________ time/MU

A

Decrease

33
Q

Increase PSF = ________ treatment time

A

Decrease

34
Q

Highest PSF

A

1.5 for large fields at orthovoltage energies (150-500 kV)

35
Q

Increase SSD = ______ in TAR because they’re at same distance

A

No change

36
Q

Decrease FS = ________ MU

A

Increase MU (less scatter so machine has to be on longer)

37
Q

2 ways dose is lost

A

Inverse square law

Attenuation

38
Q

Increase beam energy = _________ PDD/percent transmitted

A

Increase

39
Q

Increase SSD = __________ PDD

A

Increase

40
Q

Increase field size = __________ PSF because increasing field size increases scatter

A

Increase

41
Q

Increase energy = ________ PSF

A

Decrease

42
Q

Corrects for old and new SSD

Ratio of two PDDs

A

Mayneord factor (MF)

43
Q

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

A

Tissue-phantom ratio (TPR)

44
Q

MUs and dose are _________ proportional

A

Directly

45
Q

Typical breast bridge diameter

A

20-30 cm

46
Q

Percent hotspot formula

A

GD/TD

47
Q

Equivalent square formula

A

4A/P

A = area
P = perimeter
48
Q

Dmax of a Co-60, 4X, 6X, 10X, 15X and 18X beam

A 
Co-60 = 0.5 cm
4X = 1 cm
6X = 1.5 cm
10X = 2.5 cm
15 X = 3 cm
18X = 3 cm
49
Q

7 things dose distributions vary with (beam characteristics and patient)

A 
Beam energy
Calculation depth
Field size
Beam modifiers (wedges, MLCs)
Distance from source
Patient contour
Tissue inhomogeneities (lung, bone, water, etc.)
50
Q

2 contributions/components of beam

A

Primary

Scatter

51
Q

Radiation that comes directly from the source without being scattered and usually contributes most dose

A

Primary radiation

52
Q

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

A

Scatter radiation

53
Q

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

A

Increases

54
Q

Most accurate and best algorithm but takes a lot of computational power

A

Monte Carlo

55
Q

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

A

Negligible

56
Q

Homogenous phantom that is tissue equivalent

A

Water

57
Q

Dose hits surface and begins to rise to reach Dmax

A

Buildup region

58
Q

Depth where dose reaches maximum value; scatter in equal to scatter out

A

Dmax

Electronic equilibrium

59
Q

Radiation begins to attenuate and decrease as depth increases

A

Fall-off

60
Q

Distance of DDs added to distance from source

A

Dose at depth (Dd)

61
Q

Increase field size = _________ PDD because there’s more volume irradiated which contributes more scatter to the measurement point on central axis

A

Increase

RAD 400 (4 decks)

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