The document discusses radiotherapy equipment and techniques. It describes different types of linear accelerator (LINAC) machines that are used to deliver high-energy x-rays for radiation therapy. It explains how LINACs work, including the electron gun, microwave power source, and linear accelerator components. It also describes cobalt-60 radiotherapy machines and the key components of their heads to collimate and deliver gamma rays from the radioactive cobalt source. Safety features are discussed for both LINACs and cobalt machines to shield workers from radiation.

1. Medical Equipment III
Radiotherapy
Inas A. Yassine
Systems and Biomedical Engineering Department,
Faculty of Engineering - Cairo University
iyassine@eng.cu.edu.eg

2. Cancer Treatment and Radiotherapy
§ Cancer Treatment
§ Radiotherapy
§ Surgery
§ Chemotherapy
§ Radiotherapy
§ High energy x-ray that are highly penetrable
§ LINAC
§ Magnetron
§ Cyclotron
§ Cobalt

3. Diagnostic and Therapeutic X-Ray
§ Diagnostic radiology
§ uses low energy X rays for imaging
§ Radiotherapy
§ uses high energy X rays to treat tumor.
§ ionizes the water in the cell and induces formation of free
radicals which can damage of genetic material (DNA).
§ damage may be lethal and can cause death of the tumor cell.
However, often the damage is not enough to cause cell death
i.e. it is sublethal.
§ may be converted to lethal damage by repeated exposure to
radiation.
§ Normal cells are also affected adversely by radiation but have
the capacity of repair. reversible.

4. High energy X-ray

5. Beam Collimation

6. LINAC and X-ray Machines
§ Both:
§ Provide a source of electrons in an evacuated tube
§ Require accelerating voltage between the anode and cathode
– Sd ada
§ sdasad
§ Dsadsa
X-RAY LINAC
30 to 150KV 4 to 35 MV
single(0.1 to 10 sec) shot
signal
several busts of 1/156sec
repeated hundred times a
second
Have collimators Thicker collimators
Shielded Heavily shielded
information about tissue
absorption that has been
transferred to the film
The importance is about the
energy absorbed by the tumor

7. Linear Accelerator machine Schematic

8. Iso-center Treatment Planning

9. Table Movement

10. Simplified LINAC Block Diagram

11. LINAC Block Diagram

12. Electronic Gun

13. Electron Gun

14. Electron Gun Injector
Diode Electron Gun Triode Electron Gun

15. Electron Gun Injector
§ Diode Electron Gun
§ Triode Electron Gun

16. Accelerators
§ Electrostatic accelerators
§ Kinetic energy for particles in these devices is
limited by electrical breakdown
§ Oscillating field accelerators.
§ Radio frequency electromagnetic fields and
circumvent the breakdown problem

17. Microwave Power source
§ Microwave generator to accelerate
electrons
§ Magnetron
§ Klystron

18. Magnetron

19. Magnetron

20. Magnetron

21. Klystron
§ Apply an alternating current source to the grids, such that
as one grid swings positive, the other swings negative.
§ This would mean that the electrons which are approaching
the positive going grid will be speeding up, as the ones
approaching the negative going grid will be slowing down.
§ As the phase of the AC cycle changes 180 degrees, we
have the same effect, only backwards.
§ The result would be a sort of "slinky" effect, where the
electron beam is interrupted, and moves along in bursts.
This effect is known asVELOCITY MODULATION. In
German, they say that electrons are moving in "Klystern".
(CLUSTER or BUNCH). Hence, the name Klystron.
§ would be replaced by cavity resonators. Each cavity is
individually tuned, and electromagnets are placed between
cavities for focusing purposes.

22. Simplest Klystron

23. How Klystron Works

24. Klystron
• The electron gun produces a flow of
electrons.
• The bunching cavities regulate the speed
of the electrons so that they arrive in
bunches at the output cavity.
• The bunches of electrons excite
microwaves in the output cavity of the
klystron.
• The microwaves flow into the waveguide,
which transports them to the
accelerator.
• The electrons are absorbed in the beam
stop.

25. Circulator
§ One Way sign function,
§ Placed in the waveguide between the
Klystron and the accelerating structure
§ Permit the movement of the microwave
from the klystron
§ Absorbs the reflected microwave from the
accelerator
§ prevent Klystron instability and damage

26. Accelerating Waveguide
§ Waveguides are evacuated or gas filled
metallic structures of rectangular or circular
cross-section used in the transmission of
microwaves.
§ Two types of accelerating waveguide are
used in linacs:
§ Standing Waveguide
§ Traveling Waveguid

27. Traveling and Standing Waves

28. Travelling Accelerator
§ Advancing max magnetic Field to the right

29. How the Electrons are
Accelerated

30. How the Electrons are Accelerated

31. How the Electrons are
Accelerated in Traveling Wave
Guide

32. Full Microwave Travelling wave
Accelerator

33. Standing Wave
§ Shorter Structure, Less Bulky
§ E varies in a sinusoidal manner
§ Microwave fed anywhere

34. How the Electrons are
Accelerated in Standing Wave
Guide

35. Traveling versus Standing Guides

36. Focusing and Steering coils

37. Linear Accelerators
§ Particles Accelerated in Straight
Line
§ Electrostatic or RF Fields
§ PlanarWave
§ Static Case
§ Lorentz Force
§ Energy Gain
( ) ( )
( )
( ) sdEqE
qEcm
dt
d
F
k
eEE
cyL
kin
ksti
ò=D
==
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×= -
y
ygb
w
y w
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38. Linear Accelerators
§ Wideroe
§ Long for low frequency
§ Losses
§ Alvarez
§ Higher frequency
§ Higher voltages
RF Accelerators
rfii TvL
2
1
£

39. Linear Accelerators
§ Travelling Wave
§ Standing Wave

40. Synchronicity in a LINAC
The length of the ith drift tube is
where is the velocity of the particles in the ith
drift tube and is the rf period.
Australian Synchrotron Example:
Electrons at the speed of light (a valid
approximation above 5 MeV) in a 3 GHz linac
rfii TL u
2
1
£
rfT
iu
[ ] cmsTsmccTL rfrf 5103/1;/103
2
1 98
=×=×==£

41. Steering Coils

42. Bending Magnets

43. Beam Bending
§ Achromatic
§ Non- Achromatic

44. Photons Generation and
Collimation

45. Photons Uniformity

46. Dose and Beam Quality Measurement

50. Multi Leaf Collimator

54. COBLT-60 RADIOTHERAPY
MACHINES

55. Irradiation Using High Energy Gamma Rays
§ Gamma rays are
emitted from a cobalt-
60 source – a
radioactive form of
cobalt.
§ The cobalt source is
kept within a thick,
heavy metal container.
§ This container has a slit
in it to allow a narrow
beam of gamma rays to
emerge.

56. Head Basic Functions
§ Shield the source,
§ Expose the source as required,
§ Collimate the beam to the correct size.

57. Head of a Cobalt machine

58. BEAM MODIFIERS
§ Fixed wedge filters
§ Beam Collimator
§ Beam-defining light
§ Laser positioning system

59. Radiation Controls
§ Time: Minimize time of exposure to minimize
total dose. Rotate employees to restrict individual
dose.
§ Distance: Maximize distance to source to
maximize attenuation in air.The effect of distance
can be estimated from equations.
§ Shielding: Minimize exposure by placing
absorbing shield between worker and source.

60. Safety for Cobalt machines
§ Two timers gives an accurate measure of the source or
shutter transit time.
§ A door interlock mechanism
§ it is impossible to turn the beam on as long as the door is
open, and
§ if the beam is on, the source returns to the safe position as
soon as the door opens
§ Manual beam control system is to operate on the
source exposure mechanism in emergency to return it
to the beam-off condition.
§ Audible warning must also indicate when the source is
not in the fully safe state.

61. Leakage,Area Radiation,Wipes Testing
§ Leakage radiation during irradiation is measured with the
collimator closed and any residual open area blocked by an
attenuator thick enough to reduce penetration to below
1%.
§ Personal electronic radiation monitors that emit an audible
indication of dose rate may be worn as an alternative (or
preferably, in addition) to fixed monitors (IPEM 2001)
§ Contamination from a leaking source capsule,
accomplished during a regular service when accessing to
components through wiping surfaces as close as possible
to the source

62. Shielding
§ the primary beam:
§ shielding extending beyond the maximum diagonal width of
the beam as defined by the collimation system of the
equipment will be required to reduce the dose to acceptable
levels outside the treatment room for persons within the
geometrical projection of the primary beam…… A primary
barrier in the wall
§ Leakage Radiation:
§ from the target and is a consequence of the side lobes of the
polar emission of bremsstrahlung. It is attenuated by internal
lead shielding.
§ Scattered radiation:
§ arise either from the walls of the room or from the patient