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RADIOTHERAPY > TELETHERAPY > Flashcards

TELETHERAPY Flashcards

1
Q

These are the most crucial part of radiation therapy treatment

A
  • Px positioning & immobilization
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2
Q

Give 5 CHAR. OF A GOOD IMMOBILIZATION DEVICE

A
  • Ease of use
  • Ease of making the device
  • Comfort for the patient
  • Minimal space requirement for storage
  • Resistance to bending & stretching
  • Minimal perturbation of beam to not produce artifacts in image acquisition
  • Materials should minimally attenuate the radiation beam
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3
Q
  • Most common & is made of rigid plastic that becomes pliable when placed in warm water
A

AQUAPLAST/THERMOPLASTIC MASK

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4
Q

What is the advantage of using aquaplast?

A

provides great reproducibility
in daily txs, light weight and easy to
use. It can remold if the patient experiences
swelling or sudden weight loss

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5
Q
  • Custom, bean bag type pillows that are placed around the px’s body
  • air then vacuumed out of the bag for a custom fit & sealed in order to retain shape.
A

VAC LOC

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6
Q
  • Px positioned in prone as it allows the small bowel to drop below the lateral field to avoid severe side effects
A

Belly boards

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7
Q
  • Reference the radiation beam parameters
    to the px’s anatomy
A

Lasers

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8
Q
  • Uses a non-IS x-ray film or fluoroscopic machine
A

2D CONVENTIONAL RADIATION THERAPY

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9
Q

What are the landmarks used in 2d CRT?

A

bones

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10
Q
  • Uses CT-scan for planning for it allows the tumor & normal organs to be defined in 3D
  • Uses computer software to calculate the amount of radiation
A

3d Conformal radiation therapy

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11
Q

What are the 2 mechanisms that shaped the beam in 3d CRT?

A

CERROBEND BLOCKS & MLC

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12
Q
  • Multiple beams are divided into a grid-like pattern, separating the 1 big beam into numerous smaller “BEAMLETS”
  • Allows for the radiation dose to conform more precisely to the 3d shape of the tumor by modulating/controlling the intensity of the radiation beam in multiple small volumes
A

Intensity Modulated Radiation Therapy

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13
Q

What are the different safety features

A
  • Door safety interlocks
  • CCTV camera
  • Intercom system
  • Warning lights
  • EM-off Buttons (couch, gantry stand, modulator, control console)
  • Additional EM-off buttons
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14
Q
  • Uses high RF electromagnetic waves to accelerate charge particles to high energies in a LINEAR PATH inside a tube-like structured ACCELERATOR WAVEGUIDE
A

LINAC

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15
Q

What is the resonating cavity frequency of medical LINACs

A

about 3 BILLION HERTZ (cycles/sec)

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16
Q

What is the common device used with LINAC to treat cancer?

A

EBRT

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17
Q

What is the process of LINAC?

A
  • Uses microwave tech to accelerate electrons in the WAVEGUIDE, then allows these electrons to collide with a heavy metal target
  • As a result of these collision, high energy x-rays are produced from the target
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18
Q
  • Where px lays still to receive the radiation tx
A

TREATMENT COUCH/TABLE

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19
Q

What is the treatment couch/table made of?

A

carbon fiber

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20
Q
  • Gantry rotates on horizontal axis bearings located inside it
A

DRIVE STAND

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21
Q

Components of drive stand

A

klystron/magnetron
rf accelerator waveguide
water cooling system

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22
Q

preferred for higher electron energies; greater than 6 MeV

A

klystron

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23
Q

preferred for lower electron energies; 4-6 MeV

A

magnetron

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24
Q

electron tube that provides microwave to accelerate the electrons; done by amplifying introduced RF electromagnetic waves

A

 Klystron/Magnetron

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25
Q
  • Located inside the drive stand and gantry in conventional LINAC
  • Provides thermal stability to the system
A

WATER COOLING SYSTEM

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26
Q
  • Helps direct x-ray/electron beams to the patient’s tumor
A

GANTRY

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27
Q

Components of gantry

A

electron gun
accelerator structure
treatment head

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28
Q
  • Can be mounted in the gantry HORIZONTALLY FOR HIGH ENERGY single or dual energy machines w/ klytron
A

accelerator guide

29
Q

another term for accelerator guide

A

accelerator structure/ accelerator wave guide

30
Q
  • Changes the direction of the electron beam, downwards toward the patient
A

BENDING MAGNETS

31
Q
  • Bends the pulsed electron beam towards the target for x-rays/towards the scattering foil for electron treatments
A

BENDING MAGNETS

32
Q
  • Collision of electrons w/ high-density transmission-type target creates x-rays (photons) forming a forward peaking shaped x-ray beam in the direction of the px’s tumor
A

TARGET

33
Q

What is the percentage of the electron’s energy that goes into heat?

A

94%

34
Q

after the target, what are the other things the beam pass through?

A

0.25 stainless steel
10.6 mm Al electron stop
1.0 mm W beam hardener
3.0 mm steel beam hardener

35
Q

spot size of target?

A

1mm

36
Q
  • Conical shaped metal absorber that absorbs more FORWARD PEAKING PHOTONS; reduces CENTRAL EXPOSURE RATE relative that near the edge of the beam
A

BEAM FLATTENING FILTER

37
Q

What is the beam flattening filter usually made of?

A

TUNGSTEN, STEEL, LEAD, URANIUM/ALUMINUM, COPPER/BRASS

38
Q
  • Electron beams have pencil-like shape & need to be broadened to clinical useful beams and need to be made uniform.
A

scattering foils

39
Q

what is the scattering foil usually made of?

A

Aluminum or Copper

40
Q
  • Monitor integrated dose, dose rate and field symmetry.
A

IONIZATION CHAMBERS

41
Q
  • Rad beams are collimated by adjusting the upper & lower collimator jaws
A

COLLIMATORS

42
Q

What are jaws made of?

A

HIGH “Z” like tungsten/lead

43
Q
  • Heavy metal field-shaping devices w/ independent moving mechanisms used to create custom like block to spare normal tissue & direct the rad. dose to the tumor
A

MULTI-LEAF COLLIMATORS (MLC)

44
Q

what is the thickness and density of the multi-leaf collimator?

A
  • THICKNESS = 6-7.5 cm; made of a tungsten alloy; density of 17-18.5 g/cm3
45
Q
  • Deg. of conformity bet. the planned field boundary and the boundary created by the MLC depends upon:
A

 Projected leaf width
 Shape of target volume
 Angle of Collimator rotation

46
Q

Aims of shielding

A

 Protect critical organs
 Avoid unnecessary irradiation to surrounding normal tissue
 Matching adjacent fields

47
Q

Ideal shielding material characteristics

A

 High atomic no.
 High density
 Easily available
 Inexpensive

48
Q

achieved by placing sheets of lead on the surface directly. This is enough, because of the lower penetrating power of the beam

A
  • kV radiation shielding
49
Q

What are custom blocks made of?

A

LIPOWITZ METAL/CERROBEND BLOCKS

50
Q

melting point of custom blocks

A

70 deg Celsius

51
Q

density of custom blocks

A

9.4g/cm3 at 20 deg Celsius (83% of lead)

52
Q
  • Beam modifying device w/c causes a progressive decrease in intensity across beam
  • Degree of tilt depends upon slope of wedge filter.
A

WEDGE FILTERS

53
Q

material used for wedge filters

A

Tungsten, Brass, Lead or Steel

54
Q
  • Usually wedges are mounted at a distance of _______ from the skin surface
A

15 cm

55
Q

another term for bolus

A

BUILD-UP BOLUS

56
Q
  • Tissue equivalent material used to reduce the depth of the maximum dose
A

BOLUS

57
Q

ideal bolus characteristic

A

 Same electron density & atomic no.
 Pliable to conform to surface
 Usual specific gravity is 1.02-1.03

58
Q
  • COMMONLY USED MATERIALS FOR BOLUS
A

 Cotton soaked w/ water
 Paraffin wax

59
Q
  • More common approach w/c spares much of small intestine & shields spinal cord and vast majority of the kidneys from half of the beams.
A

4-field technique

60
Q

This technique is used for Superior border of pelvic portal should be at the L4-L5 interspace to include the external iliac and hypogastric lymph nodes.

A

AP PORT FIELD

61
Q

This technique Limit the dose to Urinary Bladder and Rectum in order to permit max. of intracavitary dose to gross parametrial diseases and microscopic or gross pelvic disease (nodal or tumor extension).

A

Midline shield/ midline block

62
Q

This Field allows significant protection of small bowel

A

Lateral

63
Q

what is the degree of the gantry rotation

A

360 degree

64
Q

This has more side effects than the other

A

conventional linac

65
Q

This procedure requires less room shielding requirement

A

TOMOTHERAPY

66
Q

What are the 2 beams for conventional linac?

A

x-ray (6 &15 MV)
electron (6,9,12,15,18,21 MeV)

67
Q

What is the beam for tomotheraphy

A

xray 6 MV

68
Q

whats the rotation of the conventional linac?

A

gantry rotation: limited to 360 deg

69
Q

whats the rotation for the tomotherapy

A

slip ring technology-can rotate continuously

RADIOTHERAPY (3 decks)

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