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physics > Stationary, rotating anodes and KV equipment > Flashcards

Stationary, rotating anodes and KV equipment Flashcards

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1
Q

what form of anode is used with KV

A

stationary

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2
Q

what are the advantages of a stationary anode?

A
  • constant stream of x-rays
  • constant heat production which can be removed by a cooling system
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3
Q

what is the stationary anode made from?

A

it is a solid block

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4
Q

what is the focal spot

A

where the electrons are focused, in which the x-rays are produced

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5
Q

what are the rotating advantages?

A
  • intense and instantaneous x-rays
  • clear image
  • faster, less likely to include movement
  • heat is produced across the whole area obtained when the electrons hit the target
  • tungsten is a good heat conductor, rhenium adds flexibility
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6
Q

describe the rotating anode

A
  • rotates at high speeds, if not at the correct speed, little x-rays will be produced
  • heat is dissipated by radiation
  • minimal heat is conducted due to the stem preventing the transfer of heat backwards
  • used in most imaging x-rays times
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7
Q

where is the beam less intense?

A

away from the CA

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8
Q

where do x-rays come from?

A

the applicator

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9
Q

name the equipment within a KV machine

A
  • x-ray tube
  • applicator system
  • mechanical system
  • control panel
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10
Q

what is the beam energy for kv equipment

A

50-300 kVp photons
below this won’t penetrate into the body

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11
Q

what is included within the stationary anode?

A
  • high tension power supply
  • cathode
  • anode
  • evacuated tube
  • radiation protection
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12
Q

describe superficial RT

A
  • it is low energy, which won’t penetrate the body, only a few cm deep.
  • 50-150 kVp
  • SXR = superficial X-ray
  • SXT = superficial X-ray therapy
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13
Q

what is the target made from

A

90% = tungsten
10% = rhenium

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14
Q

why is an insulator used?

A

to maintain the current

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15
Q

describe the process of the stationary anode

A
  • a current in passes through the wire
  • electrons must have enough energy to be free from the wire
  • a wire needs to be able to withstand the heat
  • a stream of electrons is targeted at the copper block
  • electrons form a negative cloud, creating an electrostatic force in all directions
  • a current will choose a path of least resistance
  • the cathode hood bunches the electrons together so it moves in a forward direction remaining in a one directional region
  • remaining in this region causes absorption back into the filament, in order for the electrons to move a more positive area needs to be created (p.d either positive or neutral)
  • stationary anode has a vacuum
  • when electrons hit the stationary anode, bremsstrahlung occurs
  • photons which pass through the edge aren’t absorbed by the anode
  • electrons which hit the target will produce EM radiation and heat
  • heat is taken away by the copper block and a oil cooling system
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16
Q

what does oil help with?

A

dissipation of heat by convection

17
Q

what is the max angle

A

30 degrees (a greater angle will cause an uneven distribution)

18
Q

a wider treatment angle?

A

has a wider width/ beam size at a shorter distance, with the intensity at G and t being lower than the CA

19
Q

what is the anode heel effect

A

it is the production of a position photon, at which it will be attenuated and absorbed at the target. Intensity at T is reduced, due to the angle. The g side can be controlled by an external shield

20
Q

what is thermionic emission?

A

it is the release of electrons from the cathode (free electrons gains more energy when they are released). Anode allows for heat conduction at the back of the copper block, in where theres an oil system - convection. Radiation will occur at the back of the block through the air.

21
Q

why is a glass envelope used?

A

it is used to withstand the heat to a greater extent, in which a ceramic insulator is incorporated at the cathode. this is small, less bulky so can move more easily.

22
Q

what is the range of energies produced by the glass envelope?

A

90 kVp - 300kVp

23
Q

what is perspex?

A

a tissue equivalent

24
Q

what is the acceptable beam transmission within the kv applicator?

A
  • beam size needs to reduce the intensity outside the useful beam to 2%
  • lead lining walls must not transmit more than 2% of the useful beam
25
Q

give more information about the kv applicator?

A
  • electron and DXR final collation is achieved within 5cm of SS
  • divergent sides are parallel with beam edges
  • the size is displayed on the side
  • final 15cm of DXR is made from perspex to enable accurate positioning. It also absorbs any secondary electrons produced in the Pb lining
26
Q

describe the superficial tube:

A
  • earth potential
  • power supply is required needs insulation
  • potential difference needs to be increase
  • high x-rays need accelerated electrons
  • ceramic tubes (unipolar= anode, bipolar = anode and cathode)
27
Q

what are the KV applicator advantages?

A
  • accurate establishment of the FSD
  • SS is normal to beam axis
  • clear indication of beam direction
  • applicator minimises penumbra
  • gentle immobilisation
28
Q

what are the KV applicator disadvantages?

A
  • easily damaged
  • large amount of storage is needed
  • individual parts so a wide range needs to be bought
  • specific sizes
  • bulky
  • expensive
  • heavy
29
Q

what only occurs with KV

A

beam hardening filtration

30
Q

describe inherent filtration

A
  • it reduces the beam intensity, in which soft photons are removed with some hard photons
  • low energies = PEA: aluminium in a great material for the removal of soft photons
  • increases the average be energy as it hardens the beam
  • copper removes the higher soft photons, whereas aluminium removes the softer soft photons
  • composite filter removes the soft photons
31
Q

what process removes the soft photons

A

PEA
copper has a high atomic number, so more PEA occurs

32
Q

where is the filter located

A

outside the X-ray tube between the tube and the applicator

33
Q

describe the beam arrangement

A
  • free to set up
  • single applied field
  • skin apposition
  • beam collimation
  • long applicators = long TT
34
Q

what is kv

A

accelerating voltage

35
Q

what is mA

A

number of photons emitted intensity

36
Q

where is DMAX within kv

A

on the skin surface, so the dermis and epidermis becomes damaged

37
Q

what are the x-ray beam benefits

A
  • single beam direction
  • single beam modification
  • meets patients needs
  • relieves linac pressures
  • individual immobilisation
  • unrestricted applicator positioning
  • independent couch
  • minimal planning

physics (25 decks)

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