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Rad 520 Physics > Exam Study Session 9/18 > Flashcards

Exam Study Session 9/18 Flashcards

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1
Q

What is good geometry?

A

Position detector so it does not measure scatter photons

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2
Q

What is ideal filtration?

A

Filtration that would remove all low energy xrays

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3
Q

Quality of xray beams is specified by_________&___________ for dx & _________&___________ for mega voltage X-rays

A

KVP (voltage) / HVL MV & PDD in water

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4
Q

HVL must be measured under___________ Condition?
Describe those conditions

A

“Good geometry”
Narrow beam and large distance between absorber and detector to avoid scatter radiation

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5
Q

Filter that must be arranged in proper order of highest atomic # closest to the target

A

Thoreaus filters ( tin, copper, aluminum, patient)

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6
Q

Half value layer equation

A

HVL = ln2/u(mew)

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7
Q

Produced during the decay process, will consist of single energy (written ev, kev, MeV)

A

Mono-energetic beams

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8
Q

Produced with x-ray generators will consist of multiple energies(written in v, kv, mv)

A

Poly energetic beams

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9
Q

Kvp output???

A
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10
Q

Kerma stands for?

A

Energy released in matter or kinetic energy released per unit mass

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11
Q

Energy transfer via radiative photons (bremsstrahlung )

A

Radiative kerma

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12
Q

Collisions between photons and charge particles results and electrons which dissipate energy vehicle collisions leading to ionization and excitation

A

Collisional kerma

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13
Q

Units of KERMA

A

Gy

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14
Q

?Defined in any medium for indirectly ionizing radiation?.

A

KERMA

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15
Q

How does KERMA relate to absorbed dose?

A

In the build up region kerma is higher than absorbed dose. Absorbed dose is greater than kerma after Dmax

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16
Q

Why is absorbed dose higher after build up region?

A

Absorbed dose takes into account back scatter.

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17
Q

How to find energy fluence?

A

(#Ofphotons x energy of photons) + (# Of photons x energy of photons)

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18
Q

1 Gy = 1 J/kg

A
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19
Q

What are limits to exposure (R)

A

Only valid for photons( xray & gamma ray)
3 mev limit
Only for air ionization

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20
Q

Occurs when the #and energy of charged particles (electrons) are equal entering & exiting the measurement volume

A

Charged particle equilibrium

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21
Q

What is CPE used to measure?

A

Exposure in ion chamber

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22
Q

How does radiation equilibrium and charge particle equilibrium differ?

A

Radiation equilibrium takes into account photons and electrons when charged particle equilibrium only accounts charged particles

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23
Q

Measure of ionization produced in air by photons

A

Exposure

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24
Q

1 Roentgen=_______C/kg of air

A

2.58x10^ -4

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25
Q

Steps of exposure & ion chamber

A
  1. Photons passes thru air and liberate electron through photon interactions.
  2. Electrons will then cause ionizations (anions and cations
  3. Ion collection plate with voltage applied to have anions go to the positive side and cations go to the negative side)
  4. This starts occurrent and a charge of either sign can be measured with an electrometer.
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26
Q

Guard electrode does what?

A

Insulator, prevents leakage, defines collection volume, prevents contamination

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27
Q

How does air density affect ion chamber readings:
Higher temp, molecules spread out (air density is lower)

A

Low reading

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28
Q

What air conditions would cause a high reading for an ion chamber

A

Low temp and high density (low temp causes more molecules to pack together and therefore cause more reactions within the ion chamber

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29
Q

FAC corrections

A

Air density changes
Ion recombination
Air attenuation of photons
Secondary chambers calibrated against FAC chambers use calibration factors

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30
Q

Ion chamber undesirable effect that arises from irradiation of chamber stem & cable

A

Stem effect

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31
Q

What type of chamber has negligible stem effect

A

Fully guarded

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32
Q

Stem effect varies w/?

A

Energy

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33
Q

What chamber has a collection volume .6cm^3

A

Farmer chamber

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34
Q

What chamber is well guarded and has 3 electrodes

A

Farmer chamber

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35
Q

What are the 3 electrodes of a farmer chamber

A

Central electrode - collector
Thimblewall - tissue equivalent ( pure graphite)
Gaurd electrode

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36
Q

What chamber uses a build up cap?

A

Thimble chamber/ farmer chamber

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37
Q

What is a type of thimble chamber and what makes it unique?

A

Farmer chamber - has three electrodes

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38
Q

What is a build up cap and purpose?

A

Solid air shell made of (polytrichlorofluorethlene)
Measure dose of different energies instead of in the build up region

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39
Q

Why is it hard to measure dose in the build up region

A

Steep gradient

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40
Q

Which of the following measure dose in the build up region

A

Extrapolation chamber

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41
Q

Other names for Parallel plate chamber?

A

plane parallel / pancake chamber

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42
Q

How do Parallel plate & extrapolation chamber differ & similar

A

Differ- extrapolation chamber has vaned electrode spacing. Parallel has even 2mm spacing

Similar - they measure dose in build up region.

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43
Q

Which of the following devices are preferred for detecting a lost source

A

GM counter

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44
Q

Which of the following used for in vivo measurements

A

TLD or diode

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45
Q

‘When positive and negative ions recombine the result in a charge created that never reaches collecting electrode

A

Ion recombination

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46
Q

What helps reduce ion recombination

A

Bias voltage approx 300 V

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47
Q

Which of the following would be a primary standard for ion chamber

A

FAC free air ion chamber

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48
Q

For Dosimeters, sensitivity to radiation is an ____

A

Ideal characteristic

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49
Q

Is it ideal for a dosimeter to have no energy dependence?

A

yes

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50
Q

Why is no saturation limit ideal for dosimeter?

A

because it could continue to read and not get maxed out

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51
Q

What dosimeter has the best spatial resolution

A

Film

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52
Q

Dosimeters with material with effective water equivalent Z is an ______

A

ideal characteristic

53
Q

Which dosimeter is not reusable

A

film

54
Q

Low cost, little processing for dose readout and reusable are

A

ideal characteristics for dosimeters

55
Q

What uses temperature rise as a dosimeter

A

calorimeter

56
Q

Dosimeter that is not sensitive, difficult to set up and has low spatial resolution

A

calorimeter

57
Q

What is a chemical dosimeter

A

Ferrous sulfate or fricke dosimeter

58
Q

TG 21 was based what machine

A

Cobalt

59
Q

Which is more simplistic and in use still, TG 21 or TG 51

A

TG 51

60
Q

Which TG is based on exposure to air kerma

A

TG 21

61
Q

Which TG is based on absorbed dose in water

A

TG 51

62
Q

Increase in source size affect on penumbra

A

direct

63
Q

increase SSD affect on penumbra

A

direct

64
Q

Increase SDD ( put collimator or shield closer to the skin) has what affect on penumbra

A

Indirect

65
Q

Fricke dosimeter uses what chemical change?

A

Fe 2+ to Fe 3+

66
Q

Fricke dosimeter uses what to determin change

A

Spectrophotometer

67
Q

TLD that is most common

A

Lithium Fluroide (LiF)

68
Q

How do TLDs work?

A

Electrons excited, become trapped in conduction band, when heated they are released and recombin in valence band, and release light

69
Q

Why is LiF used in TLDS

A

the atomic number is close to tissue equivalent and thermo luminescence

70
Q

For TLDs light released is _________ to the radiation dose

A

proportional

71
Q

Annealing removes what and is used for what dosimeter?

A

residual affects from exposure and TLDS

72
Q

heating plus slow cooling to remove residual effects of exposure to TLD to “wipe slate clean”

A

Annealing process

73
Q

Standard pre-irradiation annealing process for LiF

A

1 HR @ 400 degrees celsius
24 HR @ 80 degrees celsius

74
Q

??What removes the second peak on the glow curve for TLD and annealing process?

A

24 Hr @ 80 degrees celsius

75
Q

TLD is used for

A

In Vivo measurements

76
Q

Which dosimeter has advantages of reuable, good tissue equivalence and small?

A

TLD

77
Q

What are limitations to TLD

A

No immediate readout, low spatial resolution and fragile

78
Q

Which dosimeter works like a photomultiplier tube?

A

scintillator

79
Q

Which dosimeter fluoresces when struck by ionizing radiation

A

Scintillator

80
Q

Which dosimeter uses a P and N type junctions

A

Silicon Diodes

81
Q

What dosimeter is similar to how an ion chamber works by inducing a current, but it uses a solid instead of air?

A

Silicon Diodes

82
Q

What is the area called of a silicon diode where the P region and N region meet?

A

Depletion region

83
Q

Which dosimeter is utlizied in dosimetric QA

A

Silicon Diode

84
Q

Which dosimeter has immediate readout

A

Silicon Diodes

85
Q

Advantages to silicon diodes

A
  • immediate readout
  • small
  • sensitive
  • durable
  • used for QA (depth dose and profile)
86
Q

Which Dosimeter has the limitation of if wires are twisted (directional dependence)

A

Silicon Diodes

87
Q

Limitation of what dosimeter?
* energy dependence in photons beams
*if wires are twisted it wont read (directional dependence)
* sensitive to thermal affects
* radiation induced damage

A

Silicon Diodes

88
Q

What are disadvantages of radiographic film

A

*require developing, *dependant on photon energy
* not tissue you equivalent
* more sensitive to low energy (photoelectric effect)
*Not tissue equivalent

89
Q

What has these advantages?
*high spatial resolution
*permanent record
*inexpensive

A

Radiographic Film

90
Q

Disadvantages to Radiochromic film

A

Expensive
and insensitive to radiation (requires 10-50Gy)

91
Q

What is insensitive to radiation and requires 10-50Gy

A

Radiochromic film

92
Q

A film that is not based on silver halide but a radiosensitive monomer

A

Radiochromic film

93
Q

What would be used for QA and light radiation field.

A

Radiochromic film

94
Q

MOSFETs stands for

A

Metal oxide semiconductor-field effect transistor

95
Q

What has immediate dose reading and reusable.
Also is small and Llghtweight

A

MOSFETs

96
Q

Tx couches weight limit

A

typically 450-550 pounds

97
Q

Older couch tops had web called

A

tennis racket

98
Q

Why are new couches all carbon fiber?

A

Low Z material and therefore easier to treat thru

99
Q

Magnetron or kylstron:
Used for high energy and more expensive

A

Klystron

100
Q

Magnetron or klystron: magnifies or amplifies microwaves

A

Klystron

101
Q

Magnetron or klystron: require low energy microwave source (RF driver)

A

Klystron

102
Q

Magnetron or klystonon: electrons get exposed to a magnetic field which converts them into microwaves

A

Magnetron

103
Q

Magnetron or klystron: Converts the energy of a high voltage pulse into a high power microwave

A

Klystron

104
Q

What type of gas is in the accelerator tube

A

SF6

105
Q

What part of the linac forms the dose rate

A

modulator

106
Q

For the electron gun, what energy are electrons introduced

A

50Kv

107
Q

What type of target is in a linac?

A

Transmission target

108
Q

What type of target is in an xray tube

A

Reflection target-rotating anode

109
Q

What are the conditions at which a MU is defined

A

amount of time to deliver 1 cGy at 10x10 cm FS at DMax at 100cm away

110
Q

What collimators move in the linac

A

Secondary

111
Q

Do primary collimators move?

A

no

112
Q

Max field size set by primary collimators

A

40 x 40

113
Q

Why are secondary collimators move divergently with the beam?

A

to help reduce transmission penumbra

114
Q

How does secondary collimators moving divergently help reduce transmission penumbra

A

Keeps beam parallel to the collimator edges to help minimize penumbra

115
Q

What type of penumbra caused by variable transmission of beam through nondivergent collimator edge

A

Transmission penumbra

116
Q

What penumbra is due to the finite dimension of the source/ focal spot

A

Geometric penumbra

117
Q

Factors that influence geometric penumbra

A

beam energy, lateral transport of electrons in tissue

118
Q

Which penumbra is the spread of dose distriubtion near field borders

A

Physical penumbra

119
Q

Does ion chamber go before the flattening filter?

A

No

120
Q

Which of the following linac uses a Physical source?

A

Cobalt

121
Q

Average energy of cobalt machine?

A

1.25 me V

122
Q

Cobalt 60 is housed in what and is what size?

A

Stainless steel capsule & 1-2 cm in diameter

123
Q

How many modes of decay does cobalt 60 have & what are they?

A

2 modes: 1.17 mev / 1.33 mev

124
Q

Cobalt loses now much activity per month?

A

1%

125
Q

Betatron is also called

A

Donut

126
Q

Xray output is________ to the filament current

A

Very sensitive

127
Q

Xray output increase____________ with tube current, and________of the to tube voltage

A

Proportionally / squared

128
Q

The higher the energy of the electron bombarding the target the more__________ the direction of the xray emission

A

Forward

Rad 520 Physics (5 decks)

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