F. elements of machines used in radiation therapy Flashcards
The main parts that make up the linear accelerator are the
drive stand, gantry, treatment couch, console, electronic cabinet, and modulator
The______ contains the klystron, waveguide, circulator, and cooling system
drive stand
________ Prevents the linear accelerator from overheating
water-cooling system
the _____directs and aims photons to the patient
gantry
The three parts of the linear accelerator that can move are the gantry, collimator, and couch and they All rotate around the
isocenter
Most newer linear accelerators are calibrated to ____ SAD
100 SAD
A linac starts with a power supply, which provides ____ to the modulator
direct current (DC)
The ____ powers the microwave source (magnetron or klystron) and electron gun
modulator
Sources of microwaves in a linear accelerator come from a
klystron or a magnetron
Linear accelerators have either a klystron or a magnetron never
both
______are injected into the waveguide to accelerate electrons
microwaves
_____: Amplifies microwaves
Produces microwaves with a higher power than a magnetron
Used in linear accelerators that produce energies above 12 MV
klystron
_____: Stops microwaves from being reflected and reentering the klystron
circulator
____ : Generates microwaves
Used in machines that only require low energies
magnetron
The circulator is Located between the
klystron and waveguide
______: Generates electrons and sends them into the accelerator (waveguide) » Made of tungsten
electron gun
Electrons start at 50 keV, but then accelerate as they interact with
microwaves
____: Tube where electrons flow to the gantry under a vacuum
Accelerator structure
Accelerator structure is a Copper tube with copper discs/diaphragms inside with varying apertures and spacing between each
disc
Accelerator structure uses microwaves from klystron to
accelerate the electrons to the target
________: Used to bend electrons 90 to 270 degrees to aim them toward the target » 270-degree magnet system creates a more confined beam than the 90-degree magnet system
magnet system
Accelerator structure Contains sulfur hexafluoride (SF6) to prevent
arcing in the waveguide
________: Where the beam shape is formed and the beam output is monitored
treatment head
In photon therapy the components used in the treatment head are (in order):
target, fixed primary collimator, beam-flattening filter, ion chambers, secondary movable collimators, and slots for wedges, blocks, and compensators
Flattening filters are made of
lead, tungsten, uranium, steel, or aluminum
_____ are small chambers located in the path of the radiation beam and check the beam’s dose rate and symmetry
IOn chambers
Most ion chambers are sealed and will not be affected by
temperature or preassure
Secondary, _________ can create rectangular fields with sizes ranging from O x 0 cm to 40 x 40 cm at isocenter (usually 100 SAD)
movable collimating jaws
In _______ the components used in the treatment head are similar, but scattering foils are used instead of the target and flattening filter
electron therapy
______ spread out the 3 mm pencil electron beam to a larger area suitable for treatments
Scattering foils
Scattering foils are Typically made of a
thin metallic foil (lead)
The CT simulator consists of the
CT scanner, a flat couch top, a virtual simulation workstation, and a laser marking system
The CT scanner obtains volumetric images of the patient, which are used for
treatment planning
There are multiple generations of CT scanners, but the most current has a
rotating x-ray tube with a fixed ring of imaging detectors (internal components)
External parts of the CT gantry are the controls for
couch movements, gantry tilt, emergency off buttons, and localizing lasers
Current machines use _______(continuous x-ray rotation while the couch moves in or out during image acquisition)
helical scanning
CT simulators for radiation therapy have a ____ bore than conventional CT (70 - 85 cm)
larger
The larger bore size allows for _________to fit
positioning and immobilization devices
Larger bores allow for a larger scanned
field of view
The couch in the CT simulator must be identical to the couch used in the
treatment room
An ______ system is used to create reference marks on the patient
external laser
what is a pixel in CT
(picture element) - each cell within the matrix
2D representation of tissues
what is a voxel in CT
3d representation of tissues
-pixel x slice thickness
what is a matrix
layout of cells (pixels) in rows and columns
compared to diagnostic CT radiation CT have
-flat table top
- large bore apertures - 70 cm length
- external lasers
- immobilization
- virtual sim software
