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Dose Tolerances > Therapy Machines > Flashcards

Therapy Machines Flashcards

1
Q

Characteristics of a Superficial Unit:

A
  1. 50-150 kVp
  2. 8 mA
  3. SSD = 20cm
  4. 2000 rad/min Max
  5. dmax = surface
  6. spec’d out by Al (not kVp) - also called “aluminum beam”
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2
Q

Characteristics of an Orthovoltage Unit:

A
  1. 150-500 kVp
  2. 10-20 mA
  3. SSD = 50cm
  4. 100 rad/min
  5. dmax = surface
  6. spec’d out by Cu (not kVp) - also called “copper beam”
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3
Q

What is the range of a Superficial Unit?

A

8cm in tissue

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4
Q

What is the HVL of a Superficial Unit?

A

8mm Al

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5
Q

What is the d90 of an Orthovoltage Unit?

A

d90 = 2cm

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6
Q

What is the HVL of an Orthovoltage Unit?

A

1-4mm Cu

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7
Q

What is needed to calculate MU/time for Superficial and Orthovoltage units?

A
  1. Filter type
  2. BSF
  3. Output in Air
  4. Air gap (if present)
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8
Q

For Superficial and Orthovoltage units, what will a change in filter affect?

A

HVL and Dose Rate

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9
Q

For Superficial and Orthovoltage units, an increase in HVL will result in what?

A

increasing the PDD (beam hardening)

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10
Q

How does filtering shift a beam for Superficial and Orthovoltage units?

A

Filtering shifts the avg E to the right (max E does not change with filtration)

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11
Q

How does Co-60 decay?

A

beta- with release of 2 gamma rays

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12
Q

What initial source E is a Co-60 unit loaded with?

A

10,000 Ci

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13
Q

What is the Dose Rate of a Co-60 Unit?

A

200 cGy/min at 80cm

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14
Q

What is the dmax of a Co-60 Unit?

A

0.5cm

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15
Q

What is the source size of a Co-60 Unit, and will this create small or large penumbra?

A

ss = 1.5 - 2cm (with circle end facing pt); large penumbra

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16
Q

What are some advantages of Co-60 Units when compared to Cs-137 and Ra-226?

A
  1. Higher specific Activity
  2. Increased Output/Ci
  3. Higher E - deeper penetration
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17
Q

What are the leakage rates of Co-60?

A

OFF: 2mR/hr Avg; 10mR/hr Max
ON: 0.1% of dose in air at 100cm (same as LINAC)

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18
Q

Medical Cyclotrons accelerate ____?

A

charged particles (not electrons)

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19
Q

What energy is a Low E Cyclotrons, and what elements can they produce?

A

<18 MeV; F-18, O-15, N-13, C-11

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20
Q

What energy is a Medium E Cyclotrons, and what elements can they produce?

A

18 MeV to 40 MeV; I-123, TI-201, Pd-103

21
Q

What energy is a High E Cyclotrons, and what elements can they produce?

A

> 40 MeV; Cu-67

22
Q

What imaging agents are used for myocardial perfusion?

A

TI-201 and N-13

23
Q

What imaging agents are used for myocardial metabolism?

A

I-123

24
Q

What imaging agents are used for soft tissue tumor imaging?

A

Ga-67

25
Q

What imaging agents are used for regional glucose metabolism (besides kidneys and brain)?

A

F-18

26
Q

What imaging agents are used for blood flow (for brain)?

A

C-11

27
Q

What imaging agents are used for oxygen metabolism?

A

O-15

28
Q

General operation flow of LINAC:

A
  1. Klystron/Magnetron generate MW energy;
  2. Waveguide carries MW from Klystron to Accelerator Tube (guide);
  3. Electron gun injects e’ into Accelerator tube;
  4. MW accelerate e’ close to the speed of light;
  5. Bending Magnet directs e’ beam to tx head;
  6. e’ beam interacts with target (for x-ray) or scattering foil (for e’) to generate tx beam
29
Q

Flow of tx head for Photon production:

A
  1. e’ beam hits tungsten (or gold) target;
  2. Primary collimator;
  3. Flattening Filter;
  4. Ion chamber;
  5. Secondary collimator (jaws);
  6. Slot for hard wedge, blocks, compensators
30
Q

Flow of tx head for e’ production:

A
  1. e’ beam passes through primary collimator;
  2. Scattering Foil;
  3. Ion Chamber;
  4. Secondary collimator;
  5. Accessory Mount;
  6. Electron Applicator (cone)
31
Q

Characteristics of a Modulator:

A
  1. Pulse forming - pulse and repetition
  2. Thyratron switch
  3. Pulsed DC provided to e’ gun
  4. Pulsed DC provided to MW generator
32
Q

Characteristics of a Klystron:

A
  1. Power Amplifier (low level MW to high level MW) - requires input power
  2. High E
  3. Stable
33
Q

Characteristics of a Magnetron:

A
  1. High power oscillator
  2. Low E (<12 MeV)
  3. Circular cavity
  4. Unstable
34
Q

Material of a Accelerator Guide, why:

A

Copper cavities: heat and electric conductivity

35
Q

Characteristics of a Traveling Wave (accelerator guide):

A
  1. Long guide
  2. 75 keV
  3. Dummy load required
36
Q

Characteristics of a Standing Wave (accelerator guide):

A
  1. Short guide
  2. 150 keV
  3. NO dummy load required
37
Q

Characteristics of a circulator (isolator):

A
  1. prevents damage from reflected MW power
38
Q

Characteristics of an Electron Gun:

A
  1. Injects e’ into the Accelerator Guide
  2. Thorium impregnated Tungsten filament
  3. Copper Anode
  4. Control grid
39
Q

Characteristics of an Accelerator Guide:

A
  1. Evacuated (vacuum to keep out contaminants)

* *note: the rf wave guide has freon or SF6, NOT the accelerator guide**

40
Q

Characteristics of a Bending Magnet

A
  1. Bend e’ to 90 or 270 degrees

2. maintain small focal point

41
Q

How is output affected by Asymmetrical jaws:

A
  1. Sc is about the same
  2. Sp similar to block
  3. Changes to Off axis ratio
  4. Normalization
42
Q

Effects on dose profile when 1/2 beam blocking:

A

Energy at gradient is produced by Compton scattering - 2cm from CAX to 100% isodose line to 50% isodose line

43
Q

MLC intra-leaf transmission

A

1-2%

44
Q

MLC inter-leaf transmission

A

3-4%

45
Q

MLC Acceptance Testing:

A
  1. Actual Leaf Position
  2. Time Reach Position
  3. Radiation (intraleaf) Leakage
  4. Interleaf Leakage
  5. Beam Contamination
  6. Repeated at several gantry angles
46
Q

MLC Characteristics:

A
  1. not as accurate as Cerroban
  2. More efficient than blocks
  3. Tongue and groove effect
47
Q

Jaw Transmission

A

<1%

48
Q

Cerroban Transmission

A

3-5%

Dose Tolerances (23 decks)

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