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MED 107- MEDICAL PHYSICS II > 58. RADIOTHERAPY: LINAC > Flashcards

58. RADIOTHERAPY: LINAC Flashcards

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1
Q
  1. What does LINAC stand for?
A
  • Linear Accelerator
  • it functions very similarly to an X-Ray Tube
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2
Q
  1. What are the advantages of LINACs?
A
  • they are compact
  • they have an efficient design
  • they offer excellent versatility
  • they provide electron X-Ray therapy
  • they can also provide mega electron X-Ray therapy
  • they use a wide range of energies
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3
Q
  1. What are two other kinds of Accelerators that we use to carry out X-Ray Radiotherapy?
A
  1. Betatrons
  2. Microtrons
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4
Q
  1. How do Betatrons and Microtrons work?
A
  • the electrons are accelerated
  • they are accelerated very close to the speed of light
  • they are accelerated by electro-magnetic fields
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5
Q
  1. Why do we prefer to use LINAC over the X-Ray tube?
A
  • the X-Ray Tube produces low energy photons
  • the LINAC uses high energy photons

NB:
- we also make use of Teletherapy Cobalt units

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6
Q
  1. What do special accelerators produce?
A

MORE EXOTIC PARTICLES, SUCH AS:
- protons
- neutrons
- heavy ions

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7
Q
  1. What kind of X-Rays do we use in Radiotherapy?
A
  1. Superficial X-Rays
    - these have a voltage of 50 to 150 kV
  2. Orthovoltage X-Rays
    - these have a voltage of 150 to 500 kV

NB:
- both of these are produced by X-Ray machines

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8
Q
  1. What is an advantage of Superficial X-Rays?
A
  • they avoid deep tissue damage and injuries to the face
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9
Q
  1. What are the 5 main components of a Radiotherapeutic X-Ray machine?
A
  1. X-Ray Tube
  2. Ceiling or Floor Mount for the X-Ray Tube
  3. Target Cooling System
  4. Control Console
  5. X-Ray Power Generator
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10
Q
  1. What are Teletherapy Machines?
A
  • these are Treatment Machines
  • they incorporate Gamma Ray Sources to use in
    External Beam Radiotherapy
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11
Q
  1. What are the main components of a Teletherapy Machines?
A
  1. A Radioactive Source
  2. A Source Housing
    - with a beam collimator
    - with source movement mechanisms
  3. A Gantry
  4. A Stand
    - or a Housing Support Assembly
    (in stand alone machines)
  5. A patient support assembly
  6. A machine console
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12
Q
  1. What is the most widely used Teletherapy Source?
A
  • 60 Co Radionuclides
  • they are contained inside a Cylindrical Stainless Steel
    Capsule
  • they are sealed by Welding
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13
Q
  1. What is the purpose of the double welded seal?
A
  • it is used to prevent any leakage of the Radioactive
    material
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14
Q
  1. What is the purpose of Standard Source Capsules?
A
  • the enable the swapping of sources
  • this is from one Teletherapy to another
  • this is also from one isotope production facility to
    another
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15
Q
  1. What is the typical diameter of the Cylindrical Teletherapy Source?
A
  • it is between 1 and 2 cm
  • it has a height of about 2.5 cm
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16
Q
  1. What happens when we have a smaller source diameter?
A
  • the physical penumbra is smaller
  • the source is then more expensive
17
Q
  1. What is the Penumbra Region?
A
  • this is the rapid decrease at the edges of the
    Radiation Beam
18
Q
  1. What diameter do we usually choose the Penumbra to be?
A
  • the diameter is often 1.5 cm
  • this is a compromise between the Cost and Penumbra
19
Q
  1. What Order are the Typical Source activities?
A
  • 5000 to 10 000 Ci
  • this can also be translated to 185 to 370 TBq
20
Q
  1. What kind of dose rate does the Typical Source Activity provide?
A
  • they provide a Typical dose rate at 80 cm
  • this comes from the Teletherapy source of the order of
    1-2 Grays per minute
21
Q
  1. How often are Teletherapy sources replaced?
A
  • they are replaced within one half-life after they are
    installed
  • financial considerations often result in longer source
    usage
22
Q
  1. What is the half life of the 60 Co Radionuclide used in Teletherapy Source Decay?
A
  • they decay with a half-life of 5.26 years into 60 Nickel
  • this happens with the emission of electrons
23
Q
  1. What is the Maximum energy of the electrons emitted from the 60 Co Radionuclide ?
A
  • 320 keV
  • two gamma rays are also released
24
Q
  1. What are the energies of the two gamma rays released?
A
  • 1.17 MeV
  • 1.33 MeV
25
Q
  1. What do the emitted Gamma Rays constitute to?
A
  • the Therapy Beam
  • the electrons are absorbed in the Cobalt Source or the
    Source Capsule
26
Q
  1. Does the table make sense?
A
  • yes

MED 107- MEDICAL PHYSICS II (108 decks)

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