MV Radiation Equipment Flashcards
1
Q
Electron gun purpose and function (5)
A
- produces electrons
- heated filament = cathode
- anode perforated = allows electrons to move through
- potential difference between cathode and anode creates electric field for electrons to accelerate through
- electrons are thermionically emitted from cathode, focused into a pencil beam and accelerated through anode into waveguide
2
Q
Electromagnetic radiation and examples (8)
A
- wave energy is stored in magnetic and electric fields which are perpendicular to each other and the direction which the wave is travelling
- examples: microwaves, infrared light, radio waves, viable light, x-rays, UV light, gamma rays
3
Q
Types of accelerator fields (2)
A
- static field = x-ray tube = electron accelerates in an electric field from cathode to anode
- dynamic field = linac = electron accelerated by electric field of EM wave
4
Q
Accelerating waveguide function
A
- accelerates electrons in vacuum to reach desired energy
5
Q
Travelling waveguide accelerator (5)
A
- microwaves enter gun side and travel to high energy end
- electrons are captured and bunched so they travel in phase with microwave
- electrons gain speed
- at the end microwaves are absorbed or exit waveguide
- only 1 in 4 cavities at any given moment is suitable for acceleration (have an electric field)
6
Q
Standing wave accelerator (2)
A
- each end of waveguide is terminated with a conducting disk to reflect microwave power
- every second cavity carries no electric field (cannot accelerate electrons)
7
Q
Bending magnet purpose/function
A
- pencil electron beam hits target and emits photons at a horizontal angle
- bending magnets are used to guide electron pencil beam from horizontal to vertical before hitting target
8
Q
Bending magnet types (3)
A
- 90 degree = outdated = allows defocused electrons
- 112.5 degree = long and complex
- 270 degree = most common/modern = brings electron beam to a focus at focal spot
9
Q
Flattening filter/function (3)
A
- high Z material
- different sized for different energies
- flatten photon intensity to create a more uniform dose
10
Q
Horns (4)
A
- flattening filter creates horns
- slightly higher region of dose near edge of beam
- give s amore uniform dose at greater depths
- compensates for lower energy + penetration and increased scattering in edges of beam
11
Q
Monitor chambers (4)
A
- dose monitoring system
- two independent ionization chambers
- feedback on flatness, symmetry and centered beam
- 2 so that if one fails, other can be backup
12
Q
Collimator types (2)
A
- Primary = does not move
- Secondary (jaws and MLC’s) = creates field size and beam shaping
13
Q
Rectangular collimators/jaws
A
- creates a field size of 3 - 20cm
14
Q
MLC collimators
A
- large number of individually moving leaves (two opposing banks of 60)
- shape beam to tumour
15
Q
Wedges (2)
A
- physical wedge = internal/flying (fixed inside treatment head) or external (positioned manually)
- dynamic wedge = enhanced dynamic wedge/EDM (collimator jaws move while beam is on
16
Q
Microwaves function (3)
A
- electron beam is pulsed
- radio frequency power generation system (RF) is used to produce microwaves used in accelerating waveguide
- 2 components = power source and pulsed modulator
17
Q
Types of RF power source (2)
A
- magnetron
- klystron
18
Q
Magnetron function (3)
A
- strong pulsed DC electric field applied to central cathode and outer anodes to accelerate electrons
- electrons spiral outward interacting with EM wave
- wave causes electrons to oscillate and convert kinetic to microwave energy
19
Q
Klystron function (3)
A
- electron beam produced by cathode and an accelerating DC flows through cylindrical cavities and is collected
- first cavity bunches electrons so they arrive to next as a sequence at microwave frequency
- second cavity converts kinetic to microwave energy
