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Dosimetry Physics 1 > External Beam Radiation Therapy Units > Flashcards

External Beam Radiation Therapy Units Flashcards

1
Q

Gorillas Can Swing Over Small Mountains and Can Leap past Very Big Creeks

A

Grenz-Ray, Contact Therapy, Superficial Therapy, Orthovoltage, Supervoltage, Megavoltage, Co-60, Linear Accelerator, Van De graff, Betatron, Cyclotron

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2
Q

Grenz-Ray Therapy

A

Less than 20 kVp

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3
Q

Contact Therapy

A

40-50 kVp

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4
Q

What another name for contact therapy?

A

Endocavitary

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5
Q

Superficial Therapy

A

50-150 kVp

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6
Q

Orthovoltage

A

150-500 kVp

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7
Q

Supervoltage

A

500-1000 kVp

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8
Q

Megavoltage

A

Less than 1 MV

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9
Q

Cobalt-60

A

1.25 MeV

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10
Q

Linear Accelerator

A

4-25+ MV

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11
Q

Van De Graff

A

2-10 MV

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12
Q

Betatron

A

Up to 5 MeV

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13
Q

Cyclotron

A

up to 250 MeV

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14
Q

Grenz Rays Facts

A

10 cm SSD, Skin Lesion, Low depth penetration, HVL: .4mm Al

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15
Q

Contact Therapy Facts

A

Tx using endocavitary applicators at short distances (2cm or less), HVL: 1.5cm Al, beneficial for tumors 1-2mm, completely absorbed in 2cm of tissue

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16
Q

Superficial Therapy Facts

A

HVL: 1-8mm Al, 15-20 cm SSD, skin cancers no deeper than 5 mm, Advantageous that we can use lead to block out structures

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17
Q

Orthovoltage Therapy Facts

A

Quality adjusted using Thoraeus/thin cooper filters, HVL: 1-4mm Cu, lesion 2-3cm deep,

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18
Q

Thoraeus Filter Components

A

Tin, copper and Aluminium

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19
Q

What is the arrangement of the Thoraeus Filter from source to patient?

A

Tin, Copper and Aluminum

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20
Q

What is the primary radiological filter of the thoraeus filter?

A

Tin

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21
Q

What is the secondary filter of the thoraeus filter and its responsibility?

A

Copper and to absorb the characteristic x-rays of the tin

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22
Q

What is the tertiary filter of the thoraeus filter and its purpose?

A

Aluminum and absorb the characteristic radiation of the copper

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23
Q

How effective is the overall thoraeus filter and what does it specifically contribute to the energy spectrum?

A

Two fold and the filter shifts the energy towards the higher end of the energy spectrum and filters out the possibilities of any characteristic radiation

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24
Q

Supervoltage Therapy Facts

A

Resonant transformers are used due to the potential restrictions of conventional transformers

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25
Q

Cobalt-60 Teletherapy Facts

A

Gamma Rays, Replaced every 5.26 years, 3-5k Curie, 1.25 MeV gamma rays, 360 rotation, no low energy radiation

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26
Q

Co-60 Capsule

A

30mm Cylinder Discs, 1-2cm Diameter capsule, Capsule absorbs beta particles allowing on photons to be emitted

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27
Q

Explain the mechanism that occurs in a Co-60 machine during treatment

A

Once the source is turned on, the sources moves into the collimator opening (Unshielded) and once treatment has concluded then the source is reverted back into the shielded position

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28
Q

Explain the purpose of the collimators and their structure for Co-60 and Linacs

A

Collimators are two pair of metal blocks that are utilized to manipulate the vary size and shape of the beam by moving

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29
Q

Explain the purpose of MLC and their structure for Co-60 and Linacs

A

Multi-leaf collimators are small tungsten leaves that move independently to shape a beam and/or field. These MLC vary from size of 0.5-2cm for linacs

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30
Q

What is penumbra?

A

Blurring edges of a structure on a radiograph

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31
Q

What are the types of penumbra? (3)

A

Transmission Penumbra, Geometric Penumbra and Scattering Penumbra

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32
Q

What is Transmission Penumbra and how can you resolve it?

A

Transmission penumbra is when radiation passes through the edges of the collimator, and the solution is utilizing collimators that are angled with the beam divergence

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33
Q

What is the geometric penumbra and how can you resolve it?

A

Occurs due to source size,

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34
Q

What is the penumbra equation?

A

P(d) = S(SSD+depth- SDD)/ SDD

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35
Q

Geometric Factors of penumbra

A

Focal Point, decreases the source size, decreases the penumbra, Increase SDD, decreases the penumbra,and increase Source to film distance increases the Penumbra

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36
Q

What is scatter penumbra?

A

Penumbra that is created when interactions within a medium create scatter radiation

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37
Q

Beam Flatness

A

Flatness = (Maximum prof. - Minimum Prof/ Max Prof - Minimum Prof ) x 100%

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38
Q

Co-60 uses flattening filter. True or False?

A

False

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39
Q

Linac uses flattening filter. True or False?

A

True

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40
Q

Timer Error Facts

A

Also called the Shuttle error, known as the time in which the timer is on and dose is not being delivered and also when the dose that is being delivered as the timer is off

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41
Q

Explain why Co-60 Teletherapy doesn’t require daily constancy checks

A

Co-60 doesn’t require daily constancy checks as a source is being utilized which a decay constant, in comparison Linacs utilize electrical impulses that can vary.

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42
Q

In regards to the source, how is a Co-60 teletherapy machine deliver radiation?

A

Moving the source into the “on” position, essentially exposing the source

43
Q

What energy of photons can Linac’s produce?

A

4-25 MV

44
Q

What energy of electrons can Linacs produce?

A

4-25 MeV

45
Q

What is a Linac and how does it deliver radiation?

A

Linac’s are radiation therapy machines, that utilize microwave frequencies that accelerate particles such as electrons to high energies (3 GHz)

46
Q

What is the microwave frequency utilized for Linacs?

A

3 GHz

47
Q

General Pathway from Power Source to irradiation patient

A

Power Supply > Modulator > Magnetron/ElectroN Gun > Klystron > Wave-Guide > Accelerator Structure > Bending Magnetic > Target > Primary Collimator > Flattening Filter > Ion Chamber > Secondary Collimator > Tertiary Collimators

48
Q

Explain the process of the way X-rays are produced from Power Source to Target Transmission.

A

The Power Supply sends power to modulator, the modulator sends a pulse to the Magnetron AND Electron gun via Pulse forming network and hydrogen thyraton. The Magnetron then creates a microwave pulse that is pushed through the Klystron to amplify the wave. The wave is then guide via the wave guide to the accelerator structure. The Electron gun then injects the electrons into the accelerator structure that has the microwaves. The Electrons ride the occulating waves in the vacuumed accelerator. The speeding electrons then interact with the 270 bending magnet (Achromatic) to transmit through the target.

49
Q

Accelerator Facts

A

Highly Vacuumed Copper tube, can be traveling or standing wave

50
Q

Explain Traveling wave in the accelerator structure

A

Microwaves travel through the structure towards the high energy end and absorbed at the end to limit the reflection of the wave

51
Q

Explain Standing Wave in the accelerator

A

Each end of the accelerators have conductors that produce max reflecting waves at both ends of the structure, combine forwards and reverse create a standing wave.

52
Q

What must an accelerator structure that operates with standing waves include?

A

Circulator or isolator to prevent between the the linac and microwave source to prevent back reflection from moving into the microwave source

53
Q

What three orientations can an accelerator structure be in?

A

Vertical, Horizontal and Oblique

54
Q

Magnetron Facts

A

Microwave source, high-power oscillator, Less costly but less stable, Power low energy linacs, 2-5 MW peak power

55
Q

Klystron Facts

A

Microwave amplifier, driven by low power oscillator, Buncher and Catcher

56
Q

Explain the Buncher and Catcher in the Klystron

A

Electrons accelerated into Buncher (Energized by low microwave energy), Alternating E field lead to bunching. Theses bunched reach the catcher and electrons decelerate and KE is converted into high power microwaves 3-7 MW, high energy linacs

57
Q

Waveguide Facts

A

Copper tube that proved path for microwaves from source to accelerator structure, pressurized to prevent electrical breakdown from high power microwaves

58
Q

Electron Transport System Facts

A

Pencil beams are ejected out of the acceleratore structures and depending on the energy of the linacs, you will have electron transport system to bend the beam

59
Q

Explain the difference between low-energy and high-energy linac accelerator structures and a electron transport system

A

Low-energies typically have shorter accelerator tubes, which can directly shot the beam towards the target. However, high-energy accelerators have long tubes, which causes them to be oriented oblique or horizontal and an electron transport system to be used.

60
Q

Explain whats the purpose of the electron beam system

A

The electron beam system is utilized to redirect beams from high energy linacs towards a target via bending magnet and coils

61
Q

Bending Magnet facts.

A

Deflect electron beam towards target. Chromatic (90) and Achromatic (270), Low-energy do not need bending magnets

62
Q

Chromatic Magnet

A

Bend the magnet to spread the beam (spatial dispersion)

63
Q

Achromatic Magnet

A

Beam is refocused

64
Q

Transmission Target Facts.

A

Intercepts the beam to generate x-rays, made of tungsten, focal spot is 2-3mm, target moves out of the way for electront treatment

65
Q

How does energy and scattering distrubtion of x-rays relate?

A

Low energy has more backscatter and High Energy has more forward backscatter

66
Q

Treatment Head Layout (X-ray)

A

Target > Primary Collimator > Flattening Filter > Ion Chamber > Secondary Collimator > Tertiary Collimator

67
Q

Treatment Head Layout (Electrons)

A

Beam > Primary Collimator > Scattering Foil > Ion Chamber > Secondary Collimator > Accessory mount > Electron Applicator

68
Q

Flattening Filter Facts.

A

Makes the intensity uniform in the cross section, made of High Z material such as lead, conical shape

69
Q

Explain the shape of the distrubtion with a flattening filter

A

Hill shaped, climbs, levels out and then drops. Two high points known as the horns, beam is flattened

70
Q

Flattening Filter Free (FFF) facts.

A

Developed to deliver increase dose rates while reducing scatter, leakage and out of field doses

71
Q

Flattening Filter Pro’s and Con’s

A

Pro’s: Creates Dose Homogeneity across beam profile

Con’s: Reduced dose rate, increased scatter, increase leakage, beam hardening and neutron fluence

72
Q

Scattering Foil Facts.

A

Thin foil (less than 1 mm) of high atomic number material, Spread out the pencil beam uniformly into a broad beam of E- (coulomb scattering),

73
Q

What is the purpose of the dual foil system?

A

First foil is uniform in thickness, and second is thicker in the middle to combine for a more uniformly spread

74
Q

Explain the shape of the distrubtion with a Scattering Foil

A

Similar to the flattening filter, without the horns

75
Q

First beam collimator

A

Primary collimators that minimize the beam to its maximum diameter

76
Q

What structure is after the flattening filter/scatteirng foil?

A

Monitoring Ion Chambers

77
Q

What type of chambers are ion chamber and what purpose does the ion chamber serve?

A

Transmission chambers and monitors the dose and also the beam flatness

78
Q

What are monitor chambers made of?

A

Low Z material, thin (Al), no effect on beam

79
Q

What is the advantage of dual monitory chambers?

A

Redundancy and safety of dose delivery

80
Q

What structure follows after passing through the monitor chamber?

A

Secondary Collimator or otherwise known as the two pairs of Asymmetric jaws

81
Q

What size can the jaw sizing range from and also the thickness of the lead-tungsten of the jaws?

A

0x0 to 40x40 FS and to transmit less than 1% of primary beam

82
Q

What is the structure that follows the jaws?

A

Multileaf Collimators

83
Q

What is the purpose of MLC’s?

A

Provide irregular shaped field blocking and Intensity Modulation for IMRT

84
Q

What is Sc account for when the field is blocked?

A

Sc accounts fo the increase photon scattering from collimator increases from the tunnel exposed to radiation as the colli opens

85
Q

Where dose thE scatter radiation occur for Sc?

A

In the treatment head, secondary collimator (Jaws)

86
Q

What does Sp account for in field blocking?

A

Accounts for photon scattering due to tissue

87
Q

Where dose the scatter radiation occur for Sp?

A

Within the Patient

88
Q

In the scenario you are given a field size and blocked field equivalent, which do you use for Sc?

A

the given field as that is the scatter from the field size that is not blocked

89
Q

In the scenario you are given a field size and blocked field equivalent, which do you use for Sp?

A

the blocked field equivalent as the Sp is generated in the patient, where the FS is the blocked equivalent

90
Q

What are some addition componets with the head of the linac?

A

Light localization system and ODI

91
Q

What is the purpose of the light localization system?

A

To project the field at isocenter

92
Q

What is the purpose of the Optical Distnace Indicator?

A

Known as the rangefinder and allows for correct set up to SSD

93
Q

How photon energies and electron energies do most linacs have?

A

2 Photons and 5 Electrons

94
Q

What treatments can be given with MLC?

A

3DCRT and IMRT

95
Q

Record and Verification?

A

System database that is utilized to store machine delivery parameters

96
Q

Electronic Portal Imager (EPID)

A

Imaging system that is utilized for target setup or portal verification

97
Q

What energy does EPID utilize? (MV or KV)

A

MV

98
Q

Imaging System/On-Board Imaging (OBI)

A

Target verification in IGRT

99
Q

What energy does OBI utilize?

A

KV

100
Q

The image is typically clearer in the MV than KV. True or False

A

False

101
Q

Van de Graaf Accelerator facts.

A

Electrons sprayed onto belt and collect at the dome, high potential difference between the sphere and the ground, the potential is applied across the xray tube

102
Q

Betatron Facts.

A

Hollow Vacuum donut, placed between two AC mag poles, electrons accelerate in changing magnetic field, electrons may spiral out of orbit and hit a target producing an x-ray, 45MV

103
Q

Microtron

A

Dosimetry Physics 1 (6 decks)

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