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Radiation Therapy > Part IV [Clinical Radiation Generators] > Flashcards

Part IV [Clinical Radiation Generators] Flashcards

1
Q

List the kV therapy units

A

Grenz
Contact
Superficial
Orthovoltage
Supervoltage

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2
Q

[Filtration & HVL] Grenz

A

0.04-0.09 Al mm

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3
Q

[Filtration & HVL] Contact Therapy

A

0.5-1 mm Al

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4
Q

[Filtration & HVL] Superficial Therapy

A

1-2 mm Al
1-8 mm Al

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5
Q

[Filtration & HVL] Orthovoltage

A

1-4 mm Al

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6
Q

[Filtration & HVL] Supervoltage

A

10 mm Pb

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7
Q

[SSD] Grenz Therapy

A

None

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8
Q

[SSD] Contact Therapy

A

2 cm

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9
Q

[SSD] Superficial Therapy

A

15-20 cm

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10
Q

[SSD] Orthovoltage Therapy

A

50 cm

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11
Q

[SSD] Supervoltage Therapy

A

None

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12
Q

[Tube mA] Grenz Therapy

A

None

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13
Q

[Tube mA] Contact Therapy

A

2mA

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14
Q

[Tube mA] Superficial Therapy

A

3-8 mA

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15
Q

[Tube mA] Orthovoltage Therapy

A

10-20 mA

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16
Q

[Tube mA] Supervoltage Therapy

A

None

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17
Q

[Depth/Use] Grenz Therapy

A

Dermatological

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18
Q

[Depth/Use] Contact Therapy

A

1-2 mm

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19
Q

[Depth/Use] Superficial Therapy

A

<2-3 cm

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20
Q

[Depth/Use] Orthovoltage Therapy

A

5 cm

21
Q

[Depth/Use] Supervoltage Therapy

A

None

22
Q

[kV] Grenz Therapy

A

<20kV

23
Q

[kV] Contact Therapy

A

40-50 kV

24
Q

[kV] Superficial Therapy

A

50-150 kV

25
Q

[kV] Orthovoltage Therapy

A

150-500 kV

26
Q

[kV] Supervoltage Therapy

A

500-1000 kV

27
Q

Electrostatic accelerator to produce high energy x-rays, typically 2 MV

A

Van de Graaff generator

28
Q

Van de Graaf Operation [ChargeElectronsAsX-rays]

A
  1. Charge voltage of 20 to 40 kV is applied across a moving belt of insulating material.
  2. Electrons are sprayed onto the belt and carried to the top where they are removed by a collector
    connected to a spherical cone.
  3. As the negative charges collect on the sphere, a high potential is developed between the sphere
    and the ground. This potential is applied across the X-ray tube consisting of a filament, a series of
    metal rings, and a target.
  4. X-rays are produced when electrons strike the target.
29
Q

It is based on a principle that electron in s changing magnetic field experiences acceleration in a circular orbit

A

Betatron

30
Q

Betatron Operation A.I.M R.A.T

A
  1. Accelerating tube shaped like a hollow doughnut is placed between the poles of an alternating
    current magnet.
  2. Pulse of electrons is introduced by an INJECTOR at the instant that the alternating current
    cycle begins.
  3. As the MAGNETIC FIELD rises, the electrons experience acceleration continuously and spin with
    increasing velocity around the tube.
  4. Electrons make several thousand REVOLUTIONS and achieve maximum energy.
  5. At this instant or earlier, depending on the energy desired, the electrons are made to spiral out of
    the orbit by an additional ATTRACTIVE force.
  6. The high-energy electrons then strike a TARGET to produce ×-rays or a scattering foil to produce a
    broad beam of electrons.
31
Q

Cross between a linac and cyclotron.

A

Microtron

32
Q

Microtron Operation [E.BOOST.P.T]

A
  1. Electrons are shot into the microtron cavity from the ELECTRON GUN and are forced into circular
    orbits by the magnetic field.
  2. Each time the electron bunches arrive at the resonant cavity, they receive a BOOST of energy from
    the oscillating electric field, which causes the electron orbit to increase.
  3. A moveable deflection tube (called a PEELER) shields the
    electrons from the magnetic field and extracts the electrons from the microtron,
  4. The electrons can be guided to a TARGET to produce x-rays.
    Note: The energy of the electrons is related to where the deflection tube extracted the electrons.
33
Q

Uses high frequency EM waves to accelerate charged particles such as electrons to high energies through linear tube

A

Linac

34
Q

LINAC Generations

A

Low Energy Photons
Medium Energy Photons
High Energy Photons

35
Q

[LINAC Generation, MV] Low Energy Photons

A

4-8 MV

36
Q

[LINAC Generation, MV] Medium Energy Photons

A

10-15 MV

37
Q

[LINAC Generation, MV] High Energy Photons

A

18-25 MV

38
Q

[LINAC Generation, beam] Low Energy Photons

A

Straight-through beam

39
Q

[LINAC Generation, beam] Medium Energy Photons

A

Bent beam

40
Q

[LINAC Generation, beam] High Energy Photons

A

Dual/multiple photon energy
Achromatic bending magnet or
Scanned electron pencil beam

41
Q

LINAC Operation

A
  1. The POWER SUPPLY provides direct current (DC) power to the MODULATOR, which includes the pulse
    forming network and a switch tube known as HYDROGEN THYRATON.
  2. High voltage pulses are delivered from modulator to the MAGNETRON or KLYSTRON and simultaneously to the ELECTRON GUN
  3. Pulsed MICROWAVES produced in the magnetron or klystron are INJECTED into the accelerator
    or structure via a waveguide system.
  4. Electrons, produced by an electron gun, are also pulse injected into the accelerator structure.
  5. Sinusoidal waves mixed with microwaves and electrons
  6. Hits BENDING MAGNET
42
Q

high power generating microwave pulses devices
Cylindrical construction, having a central cathode and outer anode with resonant cavities machined out a solid copper
Used in machines 6 MV or less.
Frequency per pulse ~3000 MHz, 2 MW peak power.

A

Magnetron

43
Q

Magnetron Operation

A
  1. Cathode is heated by an inner filament and the electrons are generated by THERMIONIC EMISSION
  2. STATIC MF is applied perpendicular to the plane of the cross section of the cavities and a
    pulsed DC electric field is applied between the cathode and the anode (accelerates electrons from
    cathode to anode).
  3. Under the simultaneous influence of the magnetic field, the electrons move in complex SPIRALS
    toward the resonant cavities, RADIATING ENERGY in the form of microwaves.
    4.. The generated microwave pulses are led to the ACCELERATOR TUBE via the waveguide.
44
Q

not a generator of microwaves but rather a microwave amplifier. It needs to be driven
by a low-power microwave oscillator.
High energy linacs, 7 MW peak power.

A

Klystron

45
Q

Klystron Operation

A
  1. Electrons produced by the CATHODE are accelerated by a NEGATIVE PULSE of voltage into the first
    cavity (BUCHER cavity), which is energized by low-power microwaves
  2. The microwaves set up an alternating electric field across the cavity, which alters the velocity of the
    electrons (velocity modulation process).
  3. This results in bunching of electrons as the velocity-modulated beam passes through a field-free
    space in the drift tube
  4. Electron bunches arrive at the catcher cavity where they induce charges on the ends of the cavity
    and thereby generate a retarding electric field.
  5. Electrons suffer deceleration, and the kinetic energy of electrons is converted into high-power
    microwaves.
46
Q

Charged particles are accelerated by electric field cyclically
Charged particles fly in circular orbits in magnetic field
Radius of the orbits increases as the particle speed increases
Used for PET

A

Cyclotron

47
Q

Cyclotron Operation

A

1.The two “dees” are under vacuum and placed in a direct
current magnet.
2. An alternating potential is applied to the”dees” which causes the charged particle to gain energy.
3. These particles are accelerated to the desired energy and deflected out of the “dees” and
either passed
through to be used directly or forced to collide with a suitable target.
Note: Major disadvantage is the high cost of initial purchase and ongoing

48
Q

What machines produce
megavoltage beams?

A
  1. Van de Graaff generator
  2. Linear accelerator
  3. Betatron
  4. Microtron
  5. Teletherapy gamma ray units (cobalt-60)
49
Q

Limitations of Low Energy Machines

A

• Can not reach deep-seated tumors with an adequate dosage of radiation.
• Do not spare skin and normal tissues.

Radiation Therapy (10 decks)

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