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Radiation Theraphy > Cobalt 60 & LINAC unit > Flashcards

Cobalt 60 & LINAC unit Flashcards

1
Q

Who invented the Cobalt-60 teletherapy machine in Canada in 1950s?

A

Harold E. Johns

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2
Q

It is manufactured in the nuclear reactor by irradiation of Cobalt 59 with slow neutrons for many months.

A

Cobalt 60 source

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3
Q

Half-life of Cobalt 60

A

5.27 years

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4
Q

HVL of Cobalt 60

A

12 mm lead

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5
Q

Smaller source is preferred becos of

A

smaller penumbra

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6
Q

It is the useful beam for treatment?

A

y-ray beam

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7
Q

The y emission of 1.17 MeV and 1.33 MeV gives an average energy of?

A

1.25 MeV

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8
Q

Contaminants of y-ray beam:

A

Scattered X-ray
Bremsstrahlung X-ray
Electrons

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9
Q

Results from the interaction of y-ray with Cobalt-60 source, capsule, housing and collimator.

A

Scattered X-ray

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10
Q

Results from the interaction of B-particle with the source and the steel capsule.

A

Bremsstrahlung X-ray

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11
Q

Results from the interaction of y-ray with plastic tray that holds the block.

A

Electrons

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12
Q

Plastic tray that holds the block

A

Cerrobend Block (Lead)

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13
Q

It is the number of transformations per second for each gram of radionuclide decaying at a fixed rate.

A

Specific Activity

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14
Q

The specific activity of Cobalt-60 source ranges from about?

A

75 to 200 curies per gram

2.8 to 7.4 TBq per gram

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15
Q

The high specific activity makes it possible to fabricate a small source with high y-ray output which results in:

A
  1. Large dose rate
  2. Long SSD
  3. Smaller penumbra
  4. Improved depth dose distribution
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16
Q

A typical installation has an output of..

A

750 to 9,000 Ci

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17
Q

Output is usually measured not in Ci but in?

A

rhm (Roentgen per hour at one meter)

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18
Q

The output determines the?

A

Treatment time

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19
Q

The housing used for shielding and containing the device for positioning the source?

A

Source Head

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20
Q

The source head is a steel shell filled with?

A

Lead, Tungsten, Depleted Uranium

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21
Q

The max. exposure rate in off position at 1m distance should not exceed..

A

2 mR/hr

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22
Q

The collimator system should not transmit..

A

5% of primary beam

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23
Q

The source head has a diameter of BLANK and wieghs BLANK

A

diameter of 1 meter,

weighs 1 ton or more

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24
Q

Methods of bringing the source from OFF to ON position:

A

Rotating Wheel, Sliding Drawer, Mercury Shutter, Shutter

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25
Q

Rotation is done by a stall type motor

A

Rotating Wheel

26
Q

Pulled forward by a motor with spring coming under tension

A

Sliding Drawer

27
Q

Mercury is allowed to flow into space immediately below the source

A

Mercury Shutter

28
Q

This is fixed in front of the aperture and consisting of heavy metal alloy

A

Shutter

29
Q
  • Developed by H.E. Johns
  • Consist of a series of movable interleaved bars.
  • Made from lead-tungsten/tungsten
A

Collimator

30
Q

This provides rectangular field size. Equpped with a light localizer (that serves both as a field illuminator and range finder for SSD set-up)

A

Collimator

31
Q

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

A

Linear Accelerator

32
Q

Used to produce high energy electron beam for treating superficial tumors or for treating deep seated tumors.

A

Linear Accelerator

33
Q

Acceleration of electron is achieved either through:

A

traveling electromagnetic waves and stationary electromagnetic waves

34
Q

2 types of linear accelerator

A

direct linear accelerator and helical linear accelerator

35
Q

Major Components:

A
  1. Drive Stand
  2. Gantry
  3. Treatment Couch
  4. Console Electronic Cabinet
36
Q

Klystron, Waveguide, Circular and Cooling System

A

Drive Stand

37
Q

Electron, Accelerator Structure and Treatment Head

A

Gantry

38
Q

A special type of electronic tube that generates microwave that is introduced to accelerator structure via waveguide system.

A

Magnetron/Klystron

39
Q

This produces higher energy radiation and has longer life than magnetron

A

Klystron

40
Q

A copper tube filled with an insulating gas that conducts the microwave from the klystron or magnetron into the accelerator structure

A

Waveguide

41
Q

Directs the RF energy into the waveguide & prevents any reflected microwaves from returning to the klystron

A

Circulator

42
Q

Allows many components in the gantry and drive stand to operate at constant temperature

A

Cooling system

43
Q

Drive stand:

A

A. Magnetron/Klystron
B. Waveguide
C. Circulator
D. Cooling system

44
Q

Gantry:

A

A. Electron Gun
B. Accelerator Structure
C. Treatment Head

45
Q

Responsible for the production of electrons

A

Electron Gun

46
Q

Consist of a concave tungsten cathode backed by a tungsten heating coil

A

Electron Gun

47
Q

Electrons are the injected into the accelerator guide with an initial energy of 50keV

A

Electron Gun

48
Q

An evacuated cylindrical chamber 1 to 2 m long, divided into compartment called Resonance Cavities

A

Accelerator structure

49
Q

It has a special inner structure so that microwave power accelerates electrons in a straight path to the correct energy

A

Accelerator Structure

50
Q

Accelerator guide mounted in the gantry horizontally

A

In a High Energy Machine (18-25 MV rays)

51
Q

Accelerator guide mounted in the gantry vertically

A

In a Low Energy Machine (6 MV rays)

52
Q

Provides sufficient shieding against leakage radiation in accordance with radiation protection guidelines

A

Treatment Head

53
Q

Consist of a thick shell of high density shielding material such as lead, tungsten or lead-tungsten alloy

A

Treatment Head

54
Q

Treatment Head components:

A 
Bending magnet
X-ray target
Beam flattening filter
Dose monitoring chamber
Collimator assembly
Shadow try
Electron scattering
55
Q

It functions to bend the electron group through a net angle of approx. 90 to 270 degrees and onto the x-ray target

A

Bending magnet

56
Q

To produce x-ray, electrons are made to strike a target made of metal such as tungsten, copper or aluminum

A

X-ray target

57
Q

It equalizes the intensity of the beam over its cross section. (Made from lead, tungsten, uranium, steel and Al)

A

Beam flattening filter

58
Q

Used for electron beam therapy, the electrons are made to strike a scattering foil to scatter and flatten the beam.

A

Electron scattering foil

59
Q
  • Consist of several ion chambers or a single chamber with multiple plates
  • Functions to monitor dose rate and field sysmmetry (flatness of beam)
A

Dose monitoring chamber

60
Q

Plastic transparent tray that supports field shaping blocks for x-ray therapy

A

Shadow Tray

61
Q
  • Limits the beam and provides a continous range of field sizes from 0x0 to 40x40cm^2
  • The field size is defined by the localizing system
A

Collimator

62
Q

Treatment head consists of 2 sets of collimator:

A
  • fixed primary collimator

- movable x-ray collimator

Radiation Theraphy (6 decks)

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