Medical linac Radiotherapy

1. Medical Linear Accelerators
Dr Rajesh Kumar
RPAD BARC

2. Radiation Therapy
External Beam Therapy or
Teletherapy
BrachyTherapy or
Endocurie Therapy
Nuclear Medicine
Co-60
Mega Voltage therapy
Electron

3. X-Ray Beam Therapy
Grenz-Ray Therapy
Contact Therapy
Superficial Therapy
Medium Voltage Therapy
Deep Therapy
Soft x-ray below 20KV, low penetrating power,
Operate at potential 40-50 KV, very short distance
treatment, treatment depth not more than 1-2 mm
Operate at potential ranging from 50-150 KV, treatment
distance 15-20 cm, useful for tumors confined to about
5mm depth.
Operate at potential ranging from 200-
300 KV, treatment distance 50 cm
Operate at potential ranging from 150-200 KV

4. Grenz-therapy machine

5. Deep therapy
X-ray Machine
Superficial Therapy X-Ray Machine

6. Different applicators and filters
Orthovoltage (deep) x-ray equipment

7. Grenz
super
Ortho
contact
Co-60
Skin sparing effect: low surface dose compared to maximum dose

8. Limitations of Low Energy Machines
Can not reach deep-seated tumors
with an adequate dosage of
radiation.
Do not spare skin and normal
tissues.

9. •Photon Beam (X-Ray):
•4 MV To 22 MV.
•Single Beam.
•Dual Beams
•Electron Beam:
•Multi-Beams with
energy group between:
4- 22 MeV.

10. What is a Linear Accelerator?
•Treatment machine that uses high-frequency
electromagnetic waves to accelerate charged
particles such as electrons to high energies via a
linear tube.
Charged particles travel in straight lines as they gain
energy from an alternating electromagnetic field.
• The resonating cavity frequency of the medical linacs
is about 3 billion Hertz (cycles/sec) .
• This is the most common device to treat cancer with
external beam radiation.

11. How does it work?
• The linear accelerator (Linac),
uses microwave technology to
accelerate electrons in a part of
the linac called waveguide, then
allows these electrons to collide
with a heavy metal target. As a
result of these collisions, high
energy X-‐Rays (Photons) are
produced from the target.

12. How does it work?
• These high energy photons will be
directed to the patient’s tumor and
shaped as they exit the linac to
conform to the shape of the tumor.
• Radiation can be delivered to the
tumor from any angle by rotating
the gantry and moving the
treatment couch.

13. Early Accelerators
The first one was installed at
Hammersmith in 1952.
In 1956, the first patient was
treated at Stanford
University in the United
States.
The Linac had an 8 MV X-‐ray
beam with limited gantry
motion.
These linacs were large and
bulky.

14. 2nd Generation Linacs
• The second generation,
were isocentric units,
which can rotate 360
degrees around the
gantry axis.
• They were built between
1962 and 1982.
• They improved in
precision and accuracy of
dose delivery.

15. 3rd Generation Linacs
• Better accelerator
waveguides and
bending magnet
systems and more
beam modifying
accessories.
• Wider range of beam
energies, dose rates,
field sizes and
operating modes.
• Higher reliability and
computer driven.

16. Components

17. 1.Gantry
2.Gantry/Drive stand
3.Modulator cabinet
4.Patient Support
Assembly (PSA)
5.Control Console
Major Components of a LINAC

18. 1) Electron injection system
2) RF power generator
3) Accelerating waveguide
4) Auxiliary system
5) Beam transport system
6) Beam collimation system, and
7) Beam monitoring system
Main Beam Forming Components

19. Drive Stand
Drive Stand: a stand containing the apparatus that
drives the linear accelerator
Open on both sides with swinging doors for easy access to
gauges, valves, tanks, and buttons
Klystron/Magnetron: power source used to generate
electromagnetic waves for the accelerator guides
Waveguide: hollow tube-like structure that guide the
electromagnetic waves from the magnetron to the
accelerating guide where electrons are accelerated
Circulator: directs the RF energy into the waveguide and
prevents any reflected microwaves from returning to the
klystron
Water-cooling system: allows many components in the gantry
and drive stand to operate at a constant temperature

20. The Klystron
• Provides the
source of
microwave
power to
accelerate the
electrons.
• This is done by
amplifying
introduced Radio
Frequency (RF)
electromagnetic
waves.

21. The Magnetron
• Electron tube that
provides microwave
power to accelerate
the electrons.
• Preferred for lower
electron energies, 4
MeV to 6 MeV linacs.
• For higher energies
the Klystron is a better
choice.

22. Electron Gun
Electrons produced by thermionic emission

23. Accelerator Guide
• This is sometimes called the accelerator structure
or accelerator wave guide.
• It can be mounted in the gantry horizontally for
high energy single or dual energy machines with
klystrons.
• Can be mounted vertically for low energy
machines with magnetrons.
• The microwave power produced in the klystron
or magnetron is transported to the accelerator
structure to accelerate the pulsed electron
bunches.

24. Components of Medical LINACs

25. Linac: Configurations

26. LINAC Head: Varian

27. LINAC Head: Siemens

28. LINAC Head: Elekta

29. Gantry: responsible for
directing the photon (x-
ray) energy or electron
beam at a patients
tumor.
Electron gun: produce electrons and injects them into
the accelerator structure
Accelerator structure: a special type of wave guide in
which electrons are accelerated.
Treatment head: components designed to shape and
monitor the treatment beam

30. Pulse Forming Network:
• A pulse forming network (PFN) is an
electric circuit that accumulates electrical
energy over a comparatively long time,
then releases the stored energy in the
form of a relatively square pulse of
comparatively brief duration for various
pulsed power applications.
• The Thyratron uses these pulses as a high-‐tech
switch to deliver these pulses to the electron
gun.

31. Treatment Head:
Treatment head: components
designed to shape and monitor
the treatment beam
Bending magnet: direct the electrons
vertically toward the patient
X-ray target, Primary collimator:
designed to limit the maximum field
size, Beam flattening filter: shaped the
x-ray beam in its cross sectional
dimension, Ion chamber: monitors the
beam for its symmetry in the right-left
and inferior-superior direction,
Secondary collimators: upper and
lower collimator jaws, Field light:
outlines the dimensions of the
radiation field as it appears on the
patient, allows accurate positioning of
the radiation field in relationship to
skim marks or other reference points

32. Modulator Cabinet:
• Modulator cabinet:
contains components that
distribute and monitor
primary electrical power
and high-voltage pulses to
the magnetron or klystron
• This is the noisiest of the
linac system components
and is located inside the
treatment room.
• Contains 3 subcomponents:
• Fan Control, cooling the
power distribution system.
• The auxiliary power
distribution system, contains
the emergency off button
that shuts the power to the
linac.
• Primary power distribution
system.

33. Bending Magnet:
• Changes the direction of
the electron beam,
downwards toward the
patient.
• Bends the pulsed electron
beam towards the target
for X-‐raysor toward the
scattering foil for electron
treatments.
• Produces different beam
paths for different
energies.
• Needed for energies
greater than 6 MeV.

34. Bending Magnet
Bending magnet: bends the electron beam through a
right angle, so it ends up pointed at the patient
90 degree magnets (chromatic) have the property that any
energy spread results in spatial dispersion of the beam.
Electrons are bent in proportion with their energy, the lower
energy electrons are bent more, the higher energy electrons
less
Results in a beam that is spread from side to side according
to energy
Energy sensitive, act as energy differentiators
270 degree magnets (achromatic) designed to eliminate
spatial dispersion
So not significantly disperse the different electron energies
in the beam.

35. 90 Bending of electron beam

36. Achromatic Bending
Varian: 3x90
Siemens

37. 112.5 Slalom Bending (Elekta)

38. X-‐RayTarget:
• The collision of the electrons with the high
density transmission target creates the X-‐Rays
(photons), forming a forward peaking shaped
X-‐raybeam in the direction of the patient’s
tumor.
• The X-‐raytarget is located at the focus of the
Bending Magnet.
• 94% of the electrons energy goes into heat.

39. Linac: components
Electron
Gun
Target
Cut-away view of a standing
wave accelerating
waveguide for a 6 MV linac.
The accelerating cavities are
on the central axis, the
coupling cavities are off-
side.

41. The Water Cooling System
Located in the Drive Stand and Gantry
• Provides thermal stability
to the system.
• Allows many components
in the Drive Stand and
Gantry to operate at a
constanttemperature.

42. Beam Flattening Filter:
• It is a conical shaped metal absorber, that
absorbs more forward peaking photons than the
ones in the periphery.
• Shapes the X-‐rays in their cross sectionalshape.
• It is required to create a flattened beam of
sufficient area, uniformity and symmetry.
• It is usually made of Tungsten, Steel, Lead,
Uranium and Aluminum.
• In dual energy photon linacs, two flattening filters
are required for the low and the higher photon
energies.

43. Scattering Foils:
• The electron beams have pencil-‐like shapes.
• These narrow pencil beams need to be
broadened to clinical useful beams and need to
be made uniform.
• There is a different scattering foil for each
electron beam energy produced.
• Made out of Aluminum or Cooper.
• A thin foil (or multiple ones)are used, they are
measured in mils, i.e. 8 mils of Al is about 0.2
millimeters.

44. Carousel in Standard LINAC
Carousel

45. Monitor Ionization Chambers:
• They monitor integrated Dose, Dose Rate and
Field Symmetry.
• The radiation that leaves the X-‐RayTarget or
the electron Scattering Foils will pass through
dual monitor ionization chambers, and they
produce an ionization current.
• This ionization current is proportional to the
X-‐ray of electron beamintensity.

46. Linac: Alignment of electron beam to target

47. Linac: Electron beam steering

48. Collimators:
• The radiation beams are collimated by
adjusting the upper and lower collimator jaws.
• The jaws are made of High Z number, like
Tungsten or Lead.
• The jaws can define a rectangular shaped
beam up to 40 cm by 40 cm for X-‐raybeams.

49. Treatment Couch:
• The treatment couch
or table is where the
patient lays still to
receive the radiation
treatment.
• It moves Up/Down,
Right/Left and In/
Out.
• Robotic couches are
being used in some
linacs nowadays for
3 more degrees of
freedom.

50. Medical Linac
46

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Accelerator
Wave guide
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magnet
Carrousel with
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and foils
Transmission
Ion Chambers
MLC’s
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55. Electron beam
accelerated in
wave guide
Forward peaked X-‐ray
beam
X-‐RayTarget
Flattening
Filter
Electron
scattering foil
Secondary
Collimator jaws
X-‐rayBeam
central axis
Accessory Holder
Slot

56. Electron Beam path
Accelerated
electronbeam
X-‐ray targetremoved
Scattering Foil
Transmission
monitor ion
chambers
Accessory Mount
Electron Beam Central Axis Electron cone or
applicator

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Electron gun
Accelerator
Wave guide
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Bending
magnet
Carrousel with
fla]ening filters
and foils
Transmission
Ion Chambers
MLC’s
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58. Multi Leaf Collimators (MLC’s)
• They are heavy metal field-‐shapingdevices
with independent moving mechanisms used
to create a custom like block to spare normal
tissue and direct the radiation dose to the
tumor.
• The MLC’s became a key element in the
treatment delivery of X-‐raybeams with IMRT
(Intensity Modulated Radiation Therapy).

60. Journey of Radiotherapy Technology

61. Radiation field created using MLCs

62. Siemens
Varian
Elekta

63. Availability of MLC
MLCs are available from all the major
medical LINAC manufacturers :
Elekta
Siemens
Varian
Independent manufacturers:
BrainLab
Radionics
Direx
NOMOS
Novalis

64. MLC
Conventional
Secondary Tertiary
Singly Focused
Doubly Focused
OR
Mini Micro
Single Plane
Double Plane
OR
Miniature

65. MLC: basic information

66. RPT_72 AAPM TG50: terminology
Leaf width: small leaf dimension
perpendicular to the motion direction
(and to propagation direction)
Leaf length: leaf dimension parallel to
the motion direction (and to
propagation direction)
Leaf end: the surface of the
leaf inserted into the field along
this dimension
Leaf side: the surfaces in contact with
adjacent leaves
Height of the leaf: the dimension of
the leaf along the direction of
propagation of the primary x-ray beam
(from the top of the leaf near the x-
ray
source to the bottom of the leaf nearest
the isocenter (attenuation properties)

67. RPT_72 AAPM TG50: transmission
Leaf transmission: the reduction of
dose through the full height of the leaf
Interleaf transmission: the reduction of
dose measured along a line passing
between leaf sides
End transmission: the reduction of
dose measured along a ray passing
between the ends of opposed leaves in
their most closed position
MLC transmission: the average of leaf
and interleaf transmissions (should be
less than 2%) TPS parameter

68. MLC - leaf end shape

69. MLC – leafside: The Tongue and Groove
a tongue-and-
on is divided
f the two
• To reduce
groove des
• If a large f
into two s
treatment f
the interleaf leakage some MLCs are using
ign
ield perpendicular to the leaf motion directi
ubfields, an underdosage at the matchline o
ields is observed (IMRT, VMAT)

70. Huq et al., PMB 47, 2002

71. MLC – motion
constraints
Leaf over-travel: the maximum distance
over the beam CAX to which an MLC leaf can travel
Leaf span: the maximum distance from the tip of the
most retracted leaf to the tip of the most extended leaf

72. MLC - The Interdigitation
• It is the ability of leaves on one side of a field to interdigitate with
neighboring leaves on the opposing leaf bank
• The ends of odd-numbered leaves from the right-hand bank are
driven past the ends of even- numbered leaves from the left-hand
bank
• The Varian collimator was the first commercial system that could
perform it

73. MLC configuration in the
Treatment Head

74. MLC – Varian configuration
Terziary, 3rd level (or Add-on) Collimator

75. HEAD ASSEMBLY of Elekta LINAC
The upper jaw (Y) is
replaced by the MLC
leaves and a back-up
diaphragm (Y-back) placed
beneath the leaves follows
the leaves to provide
additional
attenuation.

76. ELEKTA MLC: Y-Jaw replacement
No. of leaves 80
Material Tungsten
Thickness (height) 7.5 cm
Arrangement Tongue and Groove
Width at isocentre 1.0 cm
Movement path Linear
End design Curved/rounded
Focusing Single
Interdigitization of opposite leaves Possible
Position Sensor Optical/CCD camera
Back-up jaw thickness 3.0 cm
Field size at isocentre 40 x 40 cm2

77. MLC – Elekta configuration
Upper Jaw replacement
MLC

78. Agility

79. MLC – Elekta design (1)
• MLC closest to source
• Rounded leaf-end Single focused
• The MLC leaves move in the y-direction
……………………………………………………………………….
• Backup collimator moving with MLCs
• A “back-up” collimator, located beneath the leaves and above the
lower jaws, augments the attenuation provided by the individual leaves
• The back-up is essentially a thin upper jaw that can be set to follow the
leaves if they are being ganged together to form a straight edge or else
set to the position of the outermost leaf if the leaves are forming a
shape

80. MLC – Elekta design (2)
• The primary advantage of the upper jaw replacement design is that the
range of motion of the leaves required to traverse the collimated field
width is smaller, allowing for a shorter leaf length and therefore a
more compact treatment head diameter
………………………………………………………………………..
• The disadvantage of having the MLC leaves so far from the
accelerator isocenter is that the leaf width must be somewhat smaller
and the tolerances on the dimensions of the leaves as well as the leaf
travel must be tighter than for other configurations.

81. The ELEKTA MLCs
Agili
ty™
Beam
ModulatorT
M
MLCi
2™
Ape
xTM

82. MLci2TM
MLCi2™
Width leaf (@iso) 10 mm
Number of leaves 80 (40 pairs)
Max field size (@iso) 40 cm x 40 cm
Over-travel 12.5 cm
Focalized single
Thickness 8.2 cm
Interdigitation yes
Penumbra < 7 mm (5 cm x 5
cm to 15 cm x 15
cm)
< 8 mm (> 15 cm x
15 cm)
RT delivery 3DCRT-IMRT-VMAT

83. MLC Elekta Beam Modulator™
Beam
Modulator™
Width leaf (@iso) 4 mm
Number of leaves 80 (40 pairs)
Max field size (@iso) 16 cm x 21 cm
Over-travel full
Focalized single
Thickness 7.5 cm
Interdigitation yes
Back-up collimator no
Penumbra < 4 mm (up to 5 cm
x 5 cm)
< 5 mm (up to 10 cm
x 10 cm)
< 6 mm (> 10 cm x
10 cm)
RT delivery 3DCRT-IMRT-VMAT

84. µMLC Elekta Apex™
Apex™ (add-on)
Width leaf (@iso) 2.5 mm
Number of leaves 112 (56 pairs)
Max field size (@iso) 12 cm x 14 cm
Over-travel ¾ field size
Focalized double
Thickness 8 cm
Interdigitation yes
Junction Tongue and groove
Penumbra < 3.5 mm
RT delivery 3DCRT-IMRT-S&S
no VMAT

85. MLC – the new Elekta configuration:
complete upper replacement
(opposite of Siemens design)

86. The Elekta MLC AgilityTM
• Number of leaves: 160
• Interdigitation: yes
• Material: W-alloy leaves
• Width (@ isocentre): 5 mm
• The leaves are mounted on dynamic leaf guides
that can move up to 15 cm; relative to the guide
the leaves can extend up to 20 cm
• Leaf sides: flat
• The gaps between the leaves: tilted to reduce overall transmission
• The single pair of diaphragms are a novel, sculpted design to reduce
their thickness where leaves will always provide additional shielding
They move perpendicular to the MLC and can over-travel the central
axis by up to 12 cm; both the leaf and diaphragm ends arerounded.

87. AgilityTM

88. Elekta MLCs
comparison

89. Leaves shift
towards the
region with
minor leakage
AgilityTM

90. AgilityTM

91. MLC – Varian configuration
• It is positioned just below the level of the standard upper and lower
jaws
• This is “ok” for maintenance actions
• Disadvantage: the added bulk and the minor clearance to the
mechanical isocenter
• Moving the MLC farther from the x-ray target requires an increase in
the size of the leaves and a longer travel distance to move from one
side of the field to the other
• The result is that such a tertiary system decreases the collision free
zone
• In IMRT, to cover large fields, it can become necessary to split the
field in 2 or 3 sub-fields (different carriage positions)

92. Clearance head
MLC Largest Block tray Wedge
Elekta 45 cm 35.3 cm 35.3 cm
Siemens 43 cm 43 cm 43 cm
Varian 42 cm 35 cm 35 cm

93. MLC – Varian design
• Rounded leaf-end
• Single focused
• No backup jaw moving with MLCs

94. MLC – Varian Millenium120TM
o The leaves travel on a carriage to extend their
movement across the field
o Leaf interdigitation: yes
o The distance between the most extended
leaf and the most retracted leaf on the same
side (carriage) can be up to 15 cm
o Max field length X-direction: 40 cm
o Max leaf retract position (from CAX): 20.1
cm
o Max leaf extend position (over CAX): -20cm
o Leaf width in the central 20 cm of field: 5
mm
o Leaf width in outer 20 cm of field: 10 mm
o Maximum speed: 2.5 cm/s
o Leaf height: 60 mm
o Leaf end radius: 80 mm
o Leaf tongue and groove offsets: 0.4mm
o W-alloy

95. Leaf motion
constraints
VARIAN Millenium120TM
Extending the leaves out to the field center is not possible
when large fields are used. This can be illustrated by a medium
field size of 20-cm width that is symmetric relative to the field
center. Here, the entire carriage can be moved so that the
leaves can extend 5 cm (the 15 cm limit minus the 10 cm half
field width) over the field center

96. MLC – Varian 2.5 mm HD120TM
• The width of the central leaves is 2.5mm
• Each side of the Varian collimator is configured with 60 leaves distributed in an 8
cm wide central region with 32x2.5 mm leaves, flanked by two 7 cm wide outer
regions with 14x5.0 mm leaves, for a total width of 22cm
• Maximum static field size: 40 x 22 cm2
• MLC mounted on Varian True BeamTM True BeamSTx
TM

97. MLC –
Siemens
configuration
Lower Jaw replacement

98. Siemens MLC
All the leaves are
independently controlled.
The leaves may be manually
positioned with an MLC hand
control.
Leaf settings can be uploaded
to an information
management Record and
Verify (R&V) system.

99. End-on view of the Siemens MLC
truncated pie shape of the leaves as well as the leaf side
shape to reduce interleaf transmission

100. SIEMENS MLC:X-Jaw Replacement
No. of leaves 58
Field size at isocentre 40 x 40 cm2
Material Tungsten
Thickness (height) 7.6 cm
Arrangement Tongue and Groove
Width at isocentre 1.0 cm – inner 27 pairs
6.5 cm – outer 2 pairs
Movement path Circular arc
End design Straight
Focusing Double
Interdigitization Not Possible
Position Sensor Linear encoders

101. •Double focused (Conic geometry)
•Lower leakage
•Minimized penumbra independent of leave
position
•Flat edges (no rounded edges)
•No gap between closed leaves
•No carriage (no IMRT segmentation in 2
fields

102. Siemens

103. MLC – Siemens design
• MLC replaces completely secondary collimator
• The leaf ends are straight and are focused on the x-raysource
• The leaf ends as well as the leaf sides match the beam divergence,
making the configuration double-focused
• Y-jaw backups each MLC segment

104. Siemens MLC leaf ends
Siemens linacs use MLCs that move in an arc
such that the flat faces of the leaf ends are
always in the same plane as the radiation focus

105. Siemens 160 MLCTM

106. Outline
 PATIENT SUPPORT
TREATMENT COUCH

107. Patient-support
• Patient support and positioning devices are designed to
implement a given treatment technique
• Important criteria include patient comfort, stability, and
reproducibility of set-up and treatment geometry that allows
accurate calculation and delivery of dose

108. Treatment couch - movements
4 degrees of movements: vertical, transversal, longitudinal, yaw
6 degrees movements: vertical, transversal, longitudinal, yaw, pitch, roll
(with remote robotic control capability)

109. Treatment couch - rotations
• PITCH: rotation around
the X-axis
• ROLL: rotation around the
Y-axis
• YAW: rotation around the
Z-axis

110. Treatment couch - tabletop
• Current linac couch has special top consisting in a carbon
fiber table
• The carbon fiber plates sandwiched with a plastic foam core
• The carbon fiber construction ensures that no metal parts
are used in the entire treatment area
Seppala, Kulmala, J App Cl Med Phys 12(4), Fall 2011

111. Elekta HexaPOD™ evo (6 DOF)
baseboard
Connexion Short
Indexing Bar
IGRT
module

112. Varian Exact™
IGRT
(4 DOF)
Varian PerfectPitchTM
(6 DOF)
Maximum pitch and roll is ± 3.0 degrees

113. HEAD ASSEMBLY OF VARIAN LINAC

114. VARIAN MLC: Tertiary
Material Tungsten
Thickness (height) 5.0 cm
Arrangement Tongue and Groove
Movement path Linear
End design Curved/rounded
Focusing Single
Interdigitization Possible
Position Sensor Linear encoders
Standard
Millennium
HDMLC

115. Design of Varian Millennium MLC
Comparatively less
Out-of-field leakage

116. Varian MLCs
-----------------------------------------------------------------------------------
Model No. Leaves Field Size Leaf widths
@ Isocenter
-----------------------------------------------------------------------------------------------------
Millennium MLC-52 52 26 x 40 cm2 10 mm
Millennium MLC-80 80 40 x 40 cm2 10 mm
Millennium MLC-120 120 40 x 40 cm2 Centre: 5 mm, 40 pairs
Periphery: 10 mm, 20 pairs
HDMLC 120 40 x 22 cm2 Centre: 2.5 mm, 32 pairs
Periphery: 5 mm, 28 pairs
BrainLAB-m3 52 10 x 10 cm2 3.0 mm, 4.5 mm,
and 5.5 mm
-----------------------------------------------------------------------------------------------------

117. Leaf Material: Tungsten Alloys

118. Comparison of leaf assembly
(End-on view)
Elekta Varian Siemens

119. A comparison of
leaf over travel
configurations

121. Direx Acculeaf: Four Bank mMLC
BEV of AccuLeaf
aperture showing both
levels
AccuSoft BEV with
Digitally
Reconstructed
Radiographs (DRR)
using AccuLeaf

122. AccuLeaf - Specifications
Number of leaves 96 leaves (4 banks in perp. orientation)
Clearance ~ 300 mm LINAC dependent
Leaf material Wolfram (high grade)
Leaf height set in two levels, 38 mm each (total 76 mm)
Leaf width - 14 inner leaves ~3.1 mm at isocentre
at isocentre ~2.6 mm effective
- 10 outer leaves ~5.3 mm at isocentre
Field size at isocentre ~ 100 x 110 mm
Max. leaf travel at isocentre ~93 mm
Max. leaf over travel at isocentre ~ 33 mm
Dimensions Diameter 550 mm
Height 135 mm
Weight Less than 29kg

123. BrainLab: mMLC (Photograph)
mMLC
Linac head

124. BrainLab: M3-mMLC
No. of leaves 52
Field size at isocentre 100 x 102 mm2
Material Tungsten with special coating
Width at isocentre 3.0 mm – central 14 pairs
4.5 mm – outer 6 pairs
5.5 mm – outermost 6 pairs
Maximum leaf speed 1.5 cm/sec
Movement path Linear/parallel to Y-jaws
End design Curved/rounded
Over travel 50 mm
Position Sensor Linear encoder
Leaf transmission < 2%
Weight 30 Kg

125. Leaf Transmission/Leakage
Secondary MLC < 2% Tertiary MLC < 5 %
MLC 6 MV
Interleaf
HE-X
Interleaf
6 MV
Avg.
HE-X
Avg.
Elekta 4.1% 4.3%
(20 MV)
1.8% 2%
(20 MV)
Varian --- --- 1.5 -
2.5%
1.5 -
2.5%
(18 MV)
Siemens 1.1% 1.4%
(10 MV)
1.0 % 1.1%
(10 MV)
Requirement : Average transmission

126. Leaf End Transmission
Transmission through the ends of abutting leaves
Elekta 51% (6 MV)
61% (20 MV)
Varian 28% (18 MV)
Siemens ---------

127. Leakage Radiation : Varian Millennium
120 and 80 Leaves MLC

128. Standard (STD) Linac and Flattening Filter Free (FFF)Linac
Linac-‐headcomponents used in a Monte Carlo Simulation.
Building a 6 MV and 10 MV FFF linac model by tuning incident
beam parameters and matching them with measured data in a
fla]ening filter removed standard linac.

129. Varian True Beam FF and FFF beams
• 3D, IMRT, IGRT, SRS, SBRT,RapidArc
• Photons with FF: 6, 10 and 15 MV
• Photons in FFF mode: 6 and 10 MV
• Electrons: 6, 9, 12, 16 and 20MeV
• Max dose rates & Dose per beam pulse:
• MU/min mGy/pulse
• 6, 10, 15 600 0.28, 0.28,0.56
• 6 FFF 1400 0.65
• 10FFF 2400 1.11
• Electrons 1000
• Cone Beam CT (CBCT)
• kV Imaging
• Electronic Imaging Device (EPID)

130. Other modern FFF linacs
Cyberknife
Thomotherapy

131. THANK YOU