Part IV [Clinical Radiation Generators] Flashcards
List the kV therapy units
Grenz
Contact
Superficial
Orthovoltage
Supervoltage
[Filtration & HVL] Grenz
0.04-0.09 Al mm
[Filtration & HVL] Contact Therapy
0.5-1 mm Al
[Filtration & HVL] Superficial Therapy
1-2 mm Al
1-8 mm Al
[Filtration & HVL] Orthovoltage
1-4 mm Al
[Filtration & HVL] Supervoltage
10 mm Pb
[SSD] Grenz Therapy
None
[SSD] Contact Therapy
2 cm
[SSD] Superficial Therapy
15-20 cm
[SSD] Orthovoltage Therapy
50 cm
[SSD] Supervoltage Therapy
None
[Tube mA] Grenz Therapy
None
[Tube mA] Contact Therapy
2mA
[Tube mA] Superficial Therapy
3-8 mA
[Tube mA] Orthovoltage Therapy
10-20 mA
[Tube mA] Supervoltage Therapy
None
[Depth/Use] Grenz Therapy
Dermatological
[Depth/Use] Contact Therapy
1-2 mm
[Depth/Use] Superficial Therapy
<2-3 cm
[Depth/Use] Orthovoltage Therapy
5 cm
[Depth/Use] Supervoltage Therapy
None
[kV] Grenz Therapy
<20kV
[kV] Contact Therapy
40-50 kV
[kV] Superficial Therapy
50-150 kV
[kV] Orthovoltage Therapy
150-500 kV
[kV] Supervoltage Therapy
500-1000 kV
Electrostatic accelerator to produce high energy x-rays, typically 2 MV
Van de Graaff generator
Van de Graaf Operation [ChargeElectronsAsX-rays]
- Charge voltage of 20 to 40 kV is applied across a moving belt of insulating material.
- Electrons are sprayed onto the belt and carried to the top where they are removed by a collector
connected to a spherical cone. - 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. - X-rays are produced when electrons strike the target.
It is based on a principle that electron in s changing magnetic field experiences acceleration in a circular orbit
Betatron
Betatron Operation A.I.M R.A.T
- Accelerating tube shaped like a hollow doughnut is placed between the poles of an alternating
current magnet. - Pulse of electrons is introduced by an INJECTOR at the instant that the alternating current
cycle begins. - As the MAGNETIC FIELD rises, the electrons experience acceleration continuously and spin with
increasing velocity around the tube. - Electrons make several thousand REVOLUTIONS and achieve maximum energy.
- 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. - The high-energy electrons then strike a TARGET to produce ×-rays or a scattering foil to produce a
broad beam of electrons.
Cross between a linac and cyclotron.
Microtron
Microtron Operation [E.BOOST.P.T]
- Electrons are shot into the microtron cavity from the ELECTRON GUN and are forced into circular
orbits by the magnetic field. - 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. - A moveable deflection tube (called a PEELER) shields the
electrons from the magnetic field and extracts the electrons from the microtron, - 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.
Uses high frequency EM waves to accelerate charged particles such as electrons to high energies through linear tube
Linac
LINAC Generations
Low Energy Photons
Medium Energy Photons
High Energy Photons
[LINAC Generation, MV] Low Energy Photons
4-8 MV
[LINAC Generation, MV] Medium Energy Photons
10-15 MV
[LINAC Generation, MV] High Energy Photons
18-25 MV
[LINAC Generation, beam] Low Energy Photons
Straight-through beam
[LINAC Generation, beam] Medium Energy Photons
Bent beam
[LINAC Generation, beam] High Energy Photons
Dual/multiple photon energy
Achromatic bending magnet or
Scanned electron pencil beam
LINAC Operation
- 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. - High voltage pulses are delivered from modulator to the MAGNETRON or KLYSTRON and simultaneously to the ELECTRON GUN
- Pulsed MICROWAVES produced in the magnetron or klystron are INJECTED into the accelerator
or structure via a waveguide system. - Electrons, produced by an electron gun, are also pulse injected into the accelerator structure.
- Sinusoidal waves mixed with microwaves and electrons
- Hits BENDING MAGNET
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.
Magnetron
Magnetron Operation
- Cathode is heated by an inner filament and the electrons are generated by THERMIONIC EMISSION
- 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). - 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.
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.
Klystron
Klystron Operation
- 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 - The microwaves set up an alternating electric field across the cavity, which alters the velocity of the
electrons (velocity modulation process). - This results in bunching of electrons as the velocity-modulated beam passes through a field-free
space in the drift tube - Electron bunches arrive at the catcher cavity where they induce charges on the ends of the cavity
and thereby generate a retarding electric field. - Electrons suffer deceleration, and the kinetic energy of electrons is converted into high-power
microwaves.
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
Cyclotron
Cyclotron Operation
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
What machines produce
megavoltage beams?
- Van de Graaff generator
- Linear accelerator
- Betatron
- Microtron
- Teletherapy gamma ray units (cobalt-60)
Limitations of Low Energy Machines
• Can not reach deep-seated tumors with an adequate dosage of radiation.
• Do not spare skin and normal tissues.
