Radiotherapy Equipment

1. ZMT 335
122/3/2017
Dr. Nik Noor Ashikin Bt Nik Ab Razak
RADIOTHERAPY & NUC MEDICINE

2. TOPIC 5 & 6
Radiotherapy Equipment
222/3/2017
Dr. Nik Noor Ashikin Bt Nik Ab Razak

3. OBJECTIVE
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To understand
the design and
functionality of
the equipment
To review
physics and
technology of
external beam
radiotherapy
equipment

4. 5.0 External Beam Equipment
5.1 Low-energy Machines
5.1.1 Superficial Equipment
5.1.2 Orthovoltage Units
5.2 Telecurie Units
5.2.1 Cs-131
5.2.2 Cobalt – 60 Unit
5.3 Linear accelerator (LINAC)
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5. 5.0 External Beam Equipment
522/3/2017 Dr. Nik Noor Ashikin Bt Nik Ab Razak

6. Therapeutic
x-ray
equipment
• 10 kVp - 150 kVp (superficial);
• 150 kVp - 400 kVp (orthovoltage/ deep)
Radioactive
sources ( γ ray
equipment)
• Cobalt 60 & Cesium 137
MV
accelerators for
X and electron
therapy
• Linear accelerator
6
5.0 External Beam Equipment

7. 5.1 Low-energy Machines
5.1.1 Superficial Equipment
5.1.2 Orthovoltage Units
722/3/2017 Dr. Nik Noor Ashikin Bt Nik Ab Razak

8. • 10-15 kVp
• Treatment of inflammatory disorders
(Langerhans’ cells), Bowen’s disease,
patchystage mycosis fungoides,
herpes simplex
1.Grenz rays
• Superficial skin lesions
• Endocavitary treatments for curative
intent (rectal)
2.Contact therapy
5.1 Low-energy Machines
•Low-energy machines: Uses x-rays generated at voltages up to 500kVp

9. • 50-150 kVp
• Skin cancer and tumors no
deeper than 0.5 cm
3.Superficial equipment
• 150-500 kVp
• Skin, mouth, and cervical
carcinoma
• Experience limitation in the
treatment of lesions deeper
than 2 to 3 cm.
4.Orthovoltage machines
5.1 Low-energy Machines

10. “conventional”
X Ray tube
with electrons
accelerated by
an electric field
filtration
important
Stationary anode
(in contrast to
diagnostic tubes
which have a
rotating anode to
allow for a smaller
focal spot)
Part 5, lecture 2: Equipment - superficial,
telecurie
10
5.1 Superficial / Orthovoltage equipment5.1 Low-energy Machines

11. 5.1 Superficial / Orthovoltage equipment
Can not reach
deep-seated
tumors with an
adequate dosage
of radiation
Do not spare
skin and
normal tissues.
LIMITATIONS
OF
LOW ENERGY
MACHINES
5.1 Low-energy Machines

12. Part 5, lecture 2: Equipment - superficial, telecurie 12
5.1 Superficial / Orthovoltage equipment
50 to 150kVp
small skin lesions
maximum applicator size
typically < 7cm
typical FSD < 30cm
beam quality measured in HVL
aluminium (0.5 to 8mm)
Superficial
150 to 500kVp
applicators or diaphragm
skin lesions, bone metastases
FSD 30 to 60cm
beam quality in HVL copper (0.2
to 5mm)
Orthovoltage
5.1 Low-energy Machines

13. 5.1.1 Superficial Equipment
1322/3/2017 Dr. Nik Noor Ashikin Bt Nik Ab Razak

14. Part 5, lecture 2: Equipment - superficial,
telecurie
14
Superficial X Ray tube (Philips RT 100)
• Manufacturers picture...
X Ray tube
Cooling
water Target
Applicator/
collimator
5.1.1 Superficial Equipment5.1.1 Superficial Equipment

15. Part 5, lecture 2: Equipment - superficial,
telecurie
15
X-ray tube
ApplicatorFilter
5.1.1 Superficial Equipment

16. X-ray
produced at
50-150 kV
Varying thickness
of filtration
(usually 1-6 mm
Al) are added to
harden the beam to
a desire degree
Superficial
treatment are
usually given
with the help of
applicators or
cones attachable
to the diaphragm
of the machine
SSD range 15
to 20 cm
5.1.1 Superficial Equipment

17. 17
Superficial x-ray equipment (cont)
• Dose is highly dependent on source-skin distance, filtration and
applicator area.
5.1.1 Superficial Equipment
15 cm FSD cones
25cm FSD cones

18. 5.1.1 Superficial Equipment5.1.1 Superficial Equipment
Usually operated
at 5-8 mA
Beyond this depth, the
dose drop-off is too
severe to deliver
adequate depth dose
without considerable
overdosing of the skin
surface
Useful for
irradiating
tumor confined
to about 5 mm
depth (~90%
depth dose)

19. 5.1.1 Superficial Equipment
• Short focus to skin distance (FSD)
and hence high output and large
influence of inverse square law
• Calibration difficult due to strong
dose gradient i.e. dose fall off and
electron contamination
Issues with
Superficial
radiotherapy

20. 5.1.2 Orthovoltage Units
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21. Uses conventional
X-ray tube
Energy range 150-
500 kV X-rays
Mostly used around
250 - 300 kVp
Applicators are used
in superficial therapy
Treatment depths of
around 20 mm
Penetration sufficient for
palliative treatment of bone
lesions relatively close to the
surface (ribs, spinal cord)
5.1.2 Orthovoltage Units5.1.2 Orthovoltage Units

22. 5.1.2 Orthovoltage Units
5.1.2 Orthovoltage Units
• Higher dose to bone - photoelectric
absorption
• Maximum dose on the surface
hence higher skin dose
• Treatment to a depth of only a few
centimeters possible
• Low energy, hence high scattered
radiation and larger penumbra
Disadvantages
Of Deep X-ray

23. 5.2 Telecurie Units
5.2.1 Cs-131
5.2.2 Cobalt – 60 Unit
2322/3/2017 Dr. Nik Noor Ashikin Bt Nik Ab Razak

24. Part 5, lecture 2: Equipment - superficial, telecurie 24
5.2 Telecurie Units
Features
of a
Teletherapy
Source
high energy
gamma ray
emission high
specific air
kerma rate
constant
simple
means of
production
Low cost
high
specific
activity
long half-
life

25. Part 5, lecture 2: Equipment - superficial, telecurie 25
5.2.1 137-Cs
137-Cs
Photon energy 0.66MeV
Relatively large source to relatively low specific activity
Medium FSD (around 60cm)
No isocentric mounting - similar to orthovoltage equipment in set-up
Not sold anymore and should not be in use

26. 5.2.2 Cobalt – 60 Unit
5.2.2.1 Properties
5.2.2.2 Application
5.2.2.3 Production
5.2.2.4 Source
5.2.2.5 Activity
5.2.2.6 Half-Life
5.2.2.7 Shielding
5.2.2.8 Penumbra
5.2.2.9 Dose Maximum
5.2.2.10 Equipment
5.2.2.10 Cobalt – 60 Equipment
5.2.2.11 Annual dose to staff
5.2.2.12 Gamma Knife 2622/3/2017 Dr. Nik Noor Ashikin Bt Nik Ab Razak

28. Part VII.14.3 : Radiation Sources in Teletherapy Slide 28
Natural Cobalt (59Co)
COBALT - Kobald, from the German for goblin or evil spirit. Discovered in 1735. Brittle hard metal similar
to iron and nickel. Found in minerals and meteorites. Salts and glass oxides are deep blue in colour.
5.2.2 Cobalt – 60 Unit

29. 5.2.2 Cobalt – 60 Unit
ORTHOVOLTAGE UNIT
150-500 KV x-rays
Maximum dose on the skin
Treatment to a depth of few centimeters
Higher absorption by bone
non uniform dose distribution
Higher side scatter hence larger penumbra
Telecobalt Unit
1.25 MeV ‫ﻻ‬ Photon
Maximum dose at depth of 5 mm
Relatively uniform dose absorption
Higher penetration deep seated tumours
Relatively uniform distribution
More of forward scatter, lesser penumbra
Mostly isocentric unit
5.2.2 Cobalt – 60 Unit

30. 5.2.2 Cobalt – 60 Unit
Linear Accelerator
4 to 21 MV photon beams
Maximum dose at higher depth with energy
No radioactive source
Radiation only when the source is switched is ON
Uniform dose absorption
1mm source – nearly point source
Small Penumbra
Electron beam of various energies possible
Telecobalt Unit
1.25 MeV ‫ﻻ‬ Photon
Maximum dose at depth of 5 mm
Source to be changed every 4 to 5 years
Leakage radiation present even while the beam is
off
Relatively uniform distribution
1-2 cm source diameter
Larger penumbra
Gamma Photon only
5.2.2 Cobalt – 60 Unit

31. 31
Introduced in the
1950’s, being replaced
by linacs.
The first practical
radiation therapy
treatment unit to
provide a significant
dose below the skin
surface and
simultaneously spare
the skin the harsh
effects of earlier
methods.
Still used in developing
countries: simpler
design, cost, little tech
support.
5.2.2 Cobalt – 60 Unit

32. 32
Photon energy
around 1.25MeV
Specific activity
large enough for
FSD of 80cm or
even 100cm
Therefore,
isocentric set-up
possible
Constantly emit
radiation
60Co source must
be shielded in a
protective housing
(source head).
source head is a
steel shell filled
with lead (may be
up to 2 ft in
diameter
PROPERTIES
5.2.2.1 Properties

33. 33
5.2.2 Cobalt – 60 Unit
5.2.2.2 Application
APPLICATION
To treat cancers of the
head and neck area,
breast, spine, and
extremities
Areas just below the skin
surface
Ideal in treating lymph nodes.

34. 34
5.2.2 Cobalt – 60 Unit
5.2.2.3 Production of Cobalt – 60
1
• Cobalt: produced in nuclear reactors by the irradiation of neutrons
of the common stable form of 59Co.
2
• The 59Co nucleus absorbs a neutron in the reactor and becomes
60Co.
3
• Radioactive 60Co produces a useful therapy beam when it
undergoes beta decay

35. 35
5.2.2 Cobalt – 60 Unit
5.2.2.3 Production of Cobalt – 60
4
• The nucleus emits a beta particle and then two photons, 1.17 MeV
and 1.33 MeV for an effective energy of 1.25 MeV
5
• 60Co  60Ni+ + B- + neutrino (v) + gamma rays
6
• Radioactive 60Co emits radiation in the form of high energy gamma
rays in an effort to return to its more stable state.

36. 36
5.2.2 Cobalt – 60 Unit5.2.2.4 Cobalt – 60 Source
Of the close to 300 natural nuclides and over 3000 artificially produced
radionuclides, only four meet the teletherapy source requirements (Co-60, Cs-137,
Eu-152, and Ra-226) and only cobalt-60 is actually used in practice.

37. 37
5.2.2 Cobalt – 60 Unit5.2.2.4 Cobalt – 60 Source
• 1 to 3 centimetersDiameter of a 60Co source
• Encased in multiple layers of welded metal to prevent
contamination of the environment and to absorb β-
particles produced by the decay process.
Source Form: Pellets of radioactive
60Co
• Smaller source with less penumbra for the same beam
intensity
• Less hazard of contamination should a source ever
become exposed to the environment.
Source Form: 60Co fused into a solid
cylinder

38. Part VII.14.3 : Radiation Sources in Teletherapy Slide 38
How does a teletherapy Cobalt source look?
3500 pellets; 275 Ci/g; 7700 Ci
5.2.2.4 Cobalt – 60 Source

39. Part VII.14.3 : Radiation Sources in Teletherapy Slide 39
Cobalt source – how does it look?
5.2.2.4 Cobalt – 60 Source

40. 40
5.2.2 Cobalt – 60 Unit5.2.2.5 Cobalt – 60 Activity
SI unit: Curies (Ci)
3.7 x 1010 Becquerel
(Bq)
1 Bq = 1 disintegration
per second
also defined in rhm units
(roentgens per hour at 1
meter)
Most sources have an
activity of 750-9000 Ci,
typically 3000-9000 Ci
used in radiation therapy

41. 41
•Half-life: the time necessary for a radioactive material to decay to half or
50% of its original intensity.
• Requires a correction factor for this decay of about 1% per month in all
treatment calculations.
• Source must be replaced at about five year intervals.
•The half-life of 60Co is 5.26 years.
5.2.2 Cobalt – 60 Unit5.2.2.6 Cobalt – 60 Half-Life

42. 42
5.2.2 Cobalt – 60 Unit5.2.2.7 Cobalt – 60 Shielding
Cerrobend (Lipowitz metal):
Lower melting point than Pb, cheaper
50% Bismuth
26.7% Lead
13.3% tin
10% Cadmium (a toxic metal can get
into bloodstream
Density ratio of Cerrobend to Lead:
1.2 cm Cerrobend to 1 cm lead.
5 HVL is needed to reduce
intensity
A thickness of 7.2 cm of
Cerrobend needed, 6 cm lead.

46. 46
• Penumbra: the area at the edge of the radiation beam at which the dose rate changes rapidly as
a function of distance from the beam axis.5.2.2 Cobalt – 60 Unit5.2.2.8 Penumbra
1
• Describes the edge of the field having full radiation intensity for the
beam compared with the area at which the intensity falls to 0.
2
• The larger the source size, the larger the penumbra
3
• Larger field sizes are necessary to cover the same amount of tissue
adequately compared to the linac.
4
• Geometric penumbra typically wide because source diameter is large
(>2cm)

48. Part 5, lecture 2: Equipment - superficial, telecurie 48
5.2.2 Cobalt – 60 Unit5.2.2.8 Penumbra

49. 49
5.2.2 Cobalt – 60 Unit5.2.2.8 Penumbra
The transmission
penumbra can be
reduced by using
satellite
collimators,
penumbra trimmers
or trimmer bars
Trimmers are
metal bars that
attenuate the
edge of the
beam providing
a sharper field
edge.
It Should be
placed no closer
than 15 cm
from the
patients skin to
reduced
electron
contamination
(increased skin
dose) by metal
devices.
Provides
enough distance
for the
secondary
electrons
produced by the
trimmer bars to
lose sufficient
energy
REDUCING PENUMBRA

52. 52
5.2.2 Cobalt – 60 Unit5.2.2.9 Dose Maximum
Dose maximum
(Dmax): when a
greater percentage
of dose occurs
below the skin
surface
Dmax is the depth
of maximum
buildup, in which
100% of the dose
is deposited
For 60Co, Dmax
occurs at 0.5 cm
below the skin
surface.

53. Part 5, lecture 2: Equipment - superficial,
telecurie
53
• Source head and transfer mechanism
5.2.2.10 Cobalt – 60 Equipment

54. Part 5, lecture 2: Equipment - superficial,
telecurie
54
5.2.2.10 Cobalt – 60 Equipment
• shield against the
primary cobalt-60
beam
Primary barriers
• shield against
leakage radiation and
radiation scattered
from the patient
Secondary barriers
Typical cobalt-60 teletherapy installation:

55. 55
11. Beam On/Beam Off
5.2.2 Cobalt – 60 Unit5.2.2.10 Cobalt – 60 Equipment
• Turning the beam on requires physically exposing the source either by
moving it into position or by removing shields around the source.
Turning the beam
• the compressor generates air pressure by pushing the source horizontally
into position over the collimator opening.
Air pressure:
• the motor rotates a wheel 180 degrees by placing the source over the
collimator opening.
Rotating wheel:

56. Part 5, lecture 2: Equipment - superficial,
telecurie
56
5.2.2.10 Cobalt – 60 Equipment

57. Part 5, lecture 2: Equipment - superficial,
telecurie
57
Picture of a Co source change
5.2.2.10 Cobalt – 60 Equipment

58. Part 5, lecture 2: Equipment - superficial,
telecurie
58
•Assume:
• 200 days, 8hours per day working time per year
• 10% of this time in treatment room
• 3 Gy h-1 typical dose averaged over all locations of the staff member in the
treatment room
•Dose = 200 x 8 x 0.1 x 3 Gy
•  0.5mGy/year (half of dose limit for general public)
5.2.2 Cobalt – 60 Unit5.2.2.11 Annual dose to staff

59. 5.2.2 Cobalt – 60 Unit5.2.2.12 GAMMA KNIFE
Therefore it is also known as the stereotactic surgery
Patient wears a specialized helmet that is surgically fixed to their skull (brain tumor
remains stationary at target point of the gamma rays)
It is placed in a circular array in a heavily shielded assembly
Aims gamma radiation through a target point in the patient's brain.
Contains 201 cobalt-60 sources of approximately 30 curies each

60. 60
Patient positioning collimator
5.2.2 Cobalt – 60 Unit5.2.2.12 GAMMA KNIFE

62. Part 5, lecture 2: Equipment - superficial,
telecurie
62
5.2.2.12 GAMMA KNIFE