CLINICAL RADIATION GENERATORS Flashcards
Adequate dose cannot be delivered to a tumor beyond this depth
Orthovoltage
<2 cm
In order for an adequate dose to be delivered to a tumor in DEEP THERAPY;
Increase beam filtration or HVL
Disadvantages of Orthovoltage Therapy
Increase absorption in bone thus, making it unsuitable for treating tumors behind bone
Increase scattering
Depth dose distribution
Skin dose
In the early days, treatments where given until..
skin becomes red or reached its radiation tolerance
Limitation of Low energy beams/machines
Decrease depth dose distributions
Do not spare skin and normal tissue
Advantages of Superficial Therapy
Limited penetration to underlying tissues
Rapid fall off
KV Therapy Units/Machines
Grenz ray therapy
Contact therapy
Superficial therapy
Orthovoltage therapy
Supervoltage therapy
water cooling system is for:
heat dissipation
Requirements for Radiation Generators
High particle energy for penetration
High particle flux for sufficient dose rate
Energy efficient
Not too expensive
Reliable
Simple to operate
Safe
Megavoltage Units/Machines
LINAC
COBALT 60
VAN DE GRAAFF
BETATRON
MICROTRON
CYCLOTRON
electrostatic machine designed to accelerate charged particles
Van de graaff
device that produces microwaves
Magnetron
- high power oscillator
- generate microwave pulses for several microseconds
- with a repitition rate of several hundred pulses
- has cylindrical construction: central cathod, outer anode, and resonant cavities
Magnetron
operate at 2 MV peak power output to power low energy LINACS (6 MV/less)
Magnetron
T/F
electrons emitted from the cathode are accelerated TOWARD the anode by the action of pulsed DC electric field
T
not a generator
microwave amplifier
klystron
buncher cavity needs to be driven by a low power microwave oscillator
Klystron
velocity of electrons is altered by
action of electric field known as velocity modulation
series of discs
irises
Advantage of Microtron to LINAC
simplicity
easy energy selection
small beam energy spread
smaller machine
electrons from the gun
velocity of 0.8 c
Used to generate high energy protons and
heavy ions for therapy.
◾Used to accelerate deuterons to produce
neutrons.
◾Used for the production of radionuclide’s . i.e.
for PET
Medical application of cyclotron
Low energy photons (4 - 8 MV)
external wedges
fixed flattening filter
isocentric mounting
single transmission ionization
symmetric jaws
begin building a LINAC
Henry Kaplan & Edward Ginzton 1952
Kaplan and Saul Rosenberg
begin trials using the LINAC with chemotherapy to treat Hodgkins disease
1st use of cyberknife
1994
High energy
Klystron
Low energy
Magnetron
uses changing field in operation
LINAC
Betatron
Cyclotron
Microtron
uses positive charge
Van de graaff
Cyclotron
applies thermionic emission
LINAC
Microtron
Betatron
Grenz ray
Contact therapy
Superficial therapy
Orthovoltage or deep therapy
Supervoltage therapy
Uses filter
LINAC
Grenz ray
Contact or Endocavitary therapy
Superficial therapy
Orthovoltage therapy
Supervoltage therapy
beam ha a continuous spectrum of:
Bremmstrahlung xrays
the penetrating power is adjusted through :
beam hardening by filtration
beam quality depends on
accelerating potential and voltage
damage DNA directly :
electric & proton
T/F
oxygen is best radiosensitizer in radthera
T
Disadvantage of Betatron
low dose
limited field size
needs large treatment room due to large size
limited motion
allow electrons to travel along the waveguide and focus the beam
small holes or irises between copper cells
who invented cobalt 60 unit in the 1950s
Dr. Harold Johns
radioactive cobalt 60 isotope was discovered by?
Glenn T. Seaborg
cobalt 60 is produced by:
irradiating or neutron bombardment of a stable cobalt (59Co) in a nuclear reactor
primary treatment for laryngeal cancer
cobalt 60
components of cobalt60 machine
gantry
machine console
patient support
radioactive source
source housing
cobalt60 source emits two photons per disintegration with energies of
1.33 MeV & 1.17 MeV
half life of cobalt60
5.26 years
uses applicators / cones for field concentration
Superficial therapy
In supervoltage, the voltage was stepped up in an efficient manner because of:
Resonant transformer
- generatws xrays from 300 to 2000 kV
Megavoltage Therapy Units
Van de graaff
Betatron
Microtron
LINAC
Cyclotron
Cobalt 60
machine using isotopes
teletherapy
cobalt60
cesium137
low energy photons 4-8 MV
external wedges
fixed flattening filter
isocentric mounting
single transmission ionization chamber
symmetric jaws
medium energy photons 10-15 MV & electrons
bent beam
dual transmission ionization chamber
electron cones
flattening filter
movable target
high energy photons 18-25 MV & electrons
achromatic magnet
automatic wedge selector
dual photon energy
dual scattering foils
made to spread the beam to get a uniform electron fluence
scattering foil
make the beam intensity uniform since LINAC ic strongly forward peaked
flattening filter
for accelerating guide and RF generator
vacuum pumping system
used for cooling the accelerating guide, target, RF
water cooling system
for pneumatic movement of the target and other beam shaping components
air pressure system
against leakage radiation
shielding
