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Intro to Rad Treatment > x-ray generator > Flashcards

x-ray generator Flashcards

1
Q

when were x-rays discovered

A

1895

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2
Q

who discovered x- rays

A

Roentgen

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3
Q

two different mechanisms by which x-rays are produced

A

bremsstrahlung x-rays and characteristic x-rays

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4
Q

process of braking radiation as a result of a radioactive collision between a high speed electron and a nucleus

A

bremsstrahlung x-rays

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5
Q

how does bremsstrahlung mechanism produce x-rays

A

as electron passes in vicinity of a nucleus, it suffers sudden deflection, the loss in energy is radiated as electromagnetic radiation.

energies are continuous

get photon as a result

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6
Q

result of bremsstrahlung interactions in terms of energy

A

complete loss of energy or partial loss of energy

the resulting photon may have up to, but not exceeding the energy of the incident electron

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7
Q

electron interacts by ejecting an orbital electron such as K, L, or M electron

A

characteristic x-rays

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8
Q

result of characteristic x-rays in terms of energy

A

energies are discrete or specific

original electron continues with an energy equals to its initial energy minus energy given to the orbital electron

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9
Q

Kilovoltage units

A 
Grenz- ray therapy
Contact therapy
Superficial therapy
Orthovoltage therapy
Supervoltage therapy
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10
Q

negative electrode

A

cathode

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11
Q

consists of a wire filament, a circuit for current, and a negatively charged focusing cup

A

cathode

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12
Q

when heated, emits electron by thermionic emission

A

tungsten filament

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13
Q

tungsten filament’s purpose

A

heats up to emit electrons by thermionic emission

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14
Q

cathode cup

A

directs electron from cathode to anode so that they strike the target in a well defined area, the focal spot

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15
Q

positive electrode

A

the anode

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16
Q

consists of thick copper rod at the end

A

the anode

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17
Q

the tungsten target consists of

A

thick copper rod

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18
Q

why is the tungsten used as the target material

A

because of high Z and high melting point

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19
Q

what is the anode consist of

A

thick copper

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20
Q

what is the cathode consist of

A

wire filament, a circuit, and a negatively charged focusing cup (to direct electron from cathode to anode)

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21
Q

anode hood

A

prevents stray electrons from striking non target tube components

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22
Q

Beryllium window and thin glass window

A

absorbs some of photon/x-rays

also called inherent filter

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23
Q

the focal spot

A

small for diagnostic x-rays and larger for therapy x-ray tube

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24
Q

removal of heat

A

achieved by circulating oil, water, air, rotating the anode in diagnostic x-ray

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25
Q

X-ray tube efficiency

A

ratio of output energy emitted as X-ray to input energy deposited by electrons

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26
Q

efficiency equation

A

9x10^-10 ZV

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27
Q

what happens to the rest of the energy

A

converts to heat

28
Q

efficiency depends on what quantities

A

output energy x- rays and input energy electrons

29
Q

what are the specifications of quality of x-ray beam

A

quality of the beam in the range of kvp is specified in terms of energy and half value layer

30
Q

what is half value layer

A

the thickness of an absorber of specific composition required to attenuate the intensity of radiation to half of its original value under the condition of good geometry

31
Q

average energy

A

1/3 of the maximum energy of kVp

32
Q

x-ray energy spectrum for bremsstrahlung (unfiltered)

A

a continuous distribution of energies for photons

33
Q

what is the purpose of added filtration

A

enriches the beam with higher energy photons by absorbing the lower energy spectrum components

34
Q

x-ray energy distribution for characteristic x-rays

A

individual discrete energies

35
Q

where is added filtration placed

A

externally to the tube, further modifies the spectrum

36
Q

relationship between added filtration and beams

A

as filtration increases, x-ray beams hardens, which leads to achievement of higher average energy, therefore leads to greater penetrating power

37
Q

inherent filtration

A

absorption of low energy photons in the target, glass walls of tube, or thin beryllium window

38
Q

what is a LINAC

A

a device that uses high frequency electromagnetic waves to accelerate charged particles such as electron to high energies through a linear tube

39
Q

electron gun (LINAC)

A

filament when heated by an electrical current, releases electrons into the space around it

40
Q

accelerator guide (LINAC)

A

energized by microwave power

mounted horizontally for high energies
mounted vertically for low energies

41
Q

circulator (LINAC)

A

prevents any microwaves from returning to the Klystron- acts like valves in veins

42
Q

Water Cooling System

A

allows components in the drive stand and gantry to operate at a constant temp by circulating water

43
Q

Microwave system magnetron

A

magnetron is a device that produces microwaves

44
Q

Klystron

A

is a microwave amplifier, not generator- driven by a low power microwave oscillator

45
Q

pros of klystron

A

higher power microwave applications due to:

  1. excellent stability
  2. load isolation
  3. high gain
46
Q

using E/M waves to accelerate electron

A

an electron will traverse a distance = 1/2 lambda in the time =1/2 period, accelerates continuously by the standing wave

47
Q

what is the function of a bending magnet

A

treatment units with a nominal90 degree or 270 degree beam bending magnet (mounted horizontally in the gantry) to redirect beam and select energy spectrum

48
Q

effects of bending magnet

A

spread of energy of the actual beam

spread of focal point at the x-ray target

49
Q

3 pole 270 bending magnet

A

limit energy spectrum exiting the magnet

refocuses electrons of correct energy

50
Q

LINAC treatment head

A
  1. primary collimator
  2. beam flattening system (flattening filter, scattering foil)
  3. Dosimetry monitoring system
  4. Moveable collimators
51
Q

beam collimation in x-ray mode

A

treatment field size is defined by the secondary collimator

52
Q

beam collimation in electron mode

A

must be achieved close to the skin surface of the patient due to their readily scatter in air

53
Q

beam flattening

A

produce a beam of uniform intensity

54
Q

flattening filter is for

A

x-rays

55
Q

scanning system or scattering foil is for

A

electrons

56
Q

what happens if flattening filter is removed

A
  1. non uniform beam profile (highest intensity at center)
  2. increase in dose rate, decrease in treatment time
  3. softening of x-ray beam (increases surface, skin dose, shift dmax toward surface)
  4. reduction in head scattered radiation
  5. less neutron production due to higher dose per MU
57
Q

Flattening Filter Free (FFF) applications

A 
small fields (SRS)
IMRT
58
Q

purpose of FFF

A
  1. higher dose rate
  2. short term treatment as an advantage in motion management, patient comfort, treatment accuracy, reduce patient and target motion
  3. beneficial for small fields and IMRT
59
Q

Scattering system

A
  1. most common for flattening method
  2. 1 or 2 metal foils are placed in beam to scatter electrons, results in spreading and flattening beam
  3. produces x-ray contamination of the electron beam
  4. initial alignment involves more mechanical adjustments
  5. components are small and cheap
60
Q

Scanning system

A
  1. a set of electromagnetic coils are placed around the beam
  2. current to the coils vary in time, beam is bent such that it sweeps the field
  3. relies on precise control of electromagnets
  4. more expensive
  5. if scanning fails and beam remains pencil beam for a long time, a high dose may be delivered to a very small volume
61
Q

Dosimetry Monitor

A

monitor dose rate, integrated dose, field flatness and symmetry

62
Q

Secondary blocking

A

after passing through ion chambers, beam is further collimated by continuously moveable X-ray collimator (produce rectangular field sizes)

63
Q

Teletherapy

A

external beam treatment in which source of radiation (gamma emitter) is at a large distance from patient

64
Q

Trimmers

A

metal bars extend downward from collimators to trim penumbra near the treatment surface by attenuating the edge of the beam, place no closer than 15 cm

65
Q

Transmission penumbra happens if the edges of the block are parallel with the central axis of the beam

A

true

Intro to Rad Treatment (3 decks)

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