STEREOTACTIC RADIOSURGERY AND DIFFERENCE BETWEEN GAMMA N X-KNIFE

1. GAMMA KNIFE &
X-KNIFE
POOJA GUPTA
BSC 3RD YEAR

2. WHAT IS
STEREOTAXY?
"Stereo tactic" (or "stereo taxy") in Greek
means movement in space.
Stereo taxy is a minimally-invasive form of
surgical intervention which makes use of
three-dimensional coordinate system
• to locate small targets inside the body and
• to perform some actions on them such as
 Ablation (removal), biopsy, injection, stimulation,
implantation, radio surgery etc.

3. • Stereotactic irradiation refers to irradiation technique that
o uses computer calculated 3-dimensional coordinates
o to deliver a prescribed dose of ionizing radiation, Using
multiple non-coplanar photon radiation beams( linac) or
radiation from multiple Co-60 source (Gamma knife)
o with extreme precision
o to stereo tactically localized lesion primarily in the brain
o but attempts have been made to extend this technique to
other parts of the body.
STEREOTACTIC IRRADIATION

4. TYPES OF STEREOTACTIC
IRRADIATION
• With regard to sessions of dose delivery stereo tactic
irradiation is divided into two categories
• Stereo tactic radio surgery (SRS)
• Stereo tactic radio therapy (SRT)
• Stereo tactic radio surgery (SRS)
– high dose is delivered in a single session
– to treat stereo tactically localized intracranial lesions using
rigid frame attachment
– while avoiding nearby normal tissue & critical structures
• Stereo tactic radio therapy (SRT)
– Delivering dose in multiple fractions
– to sterotactically localized target
– Using relocatable frame

5. CHARACTERISTICS
OF SRS
• Characteristics of stereo tactic irradiation are as
follows :-
o High doses are delivered to target volume to achieve better
tumor control.
o High degree of dose conformity
o PTVs are small & range from 1-3.5cm3 so that
• Less irradiation of normal tissue
• Less morbidity
o With requirement for
• positional accuracy +/- 1mm
• & dose delivery accuracy +/- 5%

6. • Used for malignant tumors
• Larger lesions >3cm
• Particularly important when the tumor is adjacent to
or involving vital neurological structures such as the
optic nerve or optic chiasm
• used in situations where SRS cannot be applied safely
INDICATIONS FOR
SRT

7. GAMMA KNIFE
• Gamma Knife is a treatment unit
designed specially for
intracranial radiosurgery.
• First gamma knife was built in
1967 under direction of Lars
Lekshell in Stockholm , Sweden.
• for treatment of benign disease.
• Dedicated radio surgical device for
treatment of intracranial lesions
• Multiple beams converge on the
lesion
• At intersection high dose is
delivered, while surrounding tissue
receives minimal dose.

8. REQUIREMENTS
1. Small target volume - <3-4cm diameter
2. Sharply defined volume - good imaging
3. Accurate treatment delivery with minimal errors
4. High conformality with perfect plan & delivery
5. Normal tissue sparing by accurate localization of
target

9. • To meet the requirements of radio surgery Gamma
knife should have following specifications
o It should be possible to align the target point with
unit center point within 0.5mm
o The axes of all beams should intersect at the unit
center point within 0.3mm
o The dose rate any where within the target should
not be lower than 0.5Gy/min
o Stray radiation from unit should not be hazardous
to pt. or staff
SPECIFICATIONS OF
GAMMA KNIFE

10. Principle
• It uses multiple beams of gamma radiation to focus
precisely on the lesion.
• The idea is based on the “center of arc” principle,
where the target volume is at the center of a circular
arc of rotation. Thus, the target can be approached in
three dimensions.
• The individual gamma rays are too weak to
significantly harm the cancer cells in the tumor, but
when multiple beams are focused to the same point
the target will receive the sum of radiation from the
different beams while the surrounding area only
receive a minimal dose.

12. COMPONENTS OF GAMMA UNIT
• A radiation unit with an
upper hemispherical
shield (central body)
• Lower half of
hemisphere has a
shielding door
• An operating table &
sliding cradle
• A set of four helmets
providing circular
beams with diameters
4, 8, 14, 18mm at
isocenter.
• A control unit.
• Planning system

13. Gamma Knife – Sources
Cobalt – 60 is used
Effective photon
energy is 1.25
MeV
Essentially
monoenergetic
beam
Half life – 5.27
years
HVL lead – 11 mm
Maximum specific
activity – 41.91
Gbq/mg

14. Source Configuration
Source in Gamma Knife:
12 -20 Co60 pellets each
measuring 1mm x 1mm are
stacked axially.
Placed inside a cylindrical
stainless steel capsule sealed
by welding at both ends
This is sealed inside another
stainless steel capsule
Placed inside a aluminum
container.
Source so designed so that they
have equal activity
Total activity of a gamma knife
machine usually 6000 Ci.
Pellet
Outer
stainless
steel
capsule
Inner
stainless
steel
capsule
Outer
Aluminum
covering
20
mm

15. Sources
All 201 sources (varies according to
model) in the gamma knife intersect at a
point situated at a depth of 40 cm which
is considered as the machine isocenter
Each source can produce a maximum field
size of 18 mm at this depth.
Dose rate at the isocentre is about 400
cGy/min from all sources combined.

16. It is remarkable, that the total weight of the radioactive pellets
used within the Gamma Knife (for which 44,000 pounds of steel are
required for adequate shielding) is only 5 ounces.

20. Central body
• In gamma unit , 201(varies acc to model) cobalt 60
sources housed in a cylindrical configuration in 5 rings
• The beams are collimated by a single 12cm thick
tungsten collimator ring array which is subdivided into
8 movable sector each holding 24 sources

21. Shield
• Rear shield
• Front shield for continuous shielding
• Middle shield
• Upper shield function as jaws, it can be
• Lower shield opened or closed

22. Stereotactic Frames
• Light weight aluminium box shaped head frame
defines fixed coordinate system for accurate
localization and irradiation of PTV
• The head frame serves the following purposes
-- It prevents movement of patient head during
the Treatment
-- It enables accurate reproducibility of the
treatment position for each planning and
treatment session

23. Brown Robert Wells
frame
• Head ring used for SRS
• Linear accelerator is used
for frame fixation
• Fixed for whole procedure
(localization and treatment delivery)
• Procedure is completed in a
single session

24. Gill Thomas Cosman
Frame
• Relocatable
• Individualized by bite
block system, head rest,
bracket and Velcro straps
attached to BRW frame
• Used for fractionated SRT
• There are 2 pipes which are for
suction and respiration .
• Non invasive procedure

25. Tarbell Loeffler Cosman
Pediatric frame
• An adjustable head cup fits
the frame securely to the occiput
• Ear bars provides lateral
support
• A face mask is molded around the
eyes in nasal bridge for additional repeatable
accuracy

26.  LAITINEN FRAME:
• Used for SRT
• A clip molded to nasal bridge
 LEKSHELL FRAME:
• Fixed frame
• Used for SRS
• Used in PGI Gamma Knife

27. Treatment helmet
• Acts as secondary collimator
• Helmets have removable tungsten collimator-201
• It is docked with primary collimator at time of
treatment
• The helmet defines approximate spherical dose
distribution at isocenter with nominal diameter of 4,
8, 14, 18 mm
• The point of interest in the patient is positioned at
isocenter
• Blocked by using tungsten cylinder

28. • There are 4 collimator sizes available

29. RADIATION UNIT AND COLLIMATOR
SYSTEM
• A-cross section
• B-one sector
• C-4mm collimator
• D-8mm collimator
• E-16mm collimator

31. • Frame Placement
• Image Acquisition
• Treatment
Planning
• QA & Set up
• Treatment
STEPS INVOLVED IN
SRS/SRT

32. • 1st step of stereo tactic
procedure
• remains rigidly attached
through out the procedure.
• Unique feature of frame is
that a rigid relationship b/w
pt.’s intracranial anatomy &
frame’s coordinate systems
is established
FRAME FIXATION

33. • The Depth Helmet provides quantitative
quality assurance for relocatable head
rings (GTC).
• Checks that head ring has not moved b/w
CT scanning & treatment delivery.
• confirms that head rings have been
accurately repositioned on patient prior
to each SRT treatment.
• A Depth Probe with millimeter scale
passed into the guide tubes on the
helmet to measure distance from the
hole to the patient's head with millimeter
accuracy.
• This measurement data provides a
permanent and precise record of
positional accuracy for every treatment
DEPTH HELMET

35. • It provides foundation for treatment planning.
• Imaging modalities & techniques selected for optimum target
localization are determined by nature of target & surrounding
sts.
• Usually more than one imaging modalities are required to link
target vol. to stereo tactic frame coordinate system
• Scanning the pt. with two independent imaging modalities
provides a means of cross checking the stereo tactic coordinate
systems
• Each modality uses a specially designed localization box which
fits over pt.’s head & attaches to the frame.
• The localization box produces a set of fiducial marks on each
image that are used by planning system to link image to stereo
tactic coordinate system
IMAGE ACQUISITION

36. IMAGING
MODALITIES

37. • CT localizer frame has nine
fiducial rods that appear as dots
in trans axial slice.
• Double contrast axial images
with slice thickness 1.5-3mm for
clear delineation of tumor.
• Gives detailed information of
bony structures
• Better delineation of target
vol.& surrounding st. in relation
to external contour
• Gives quantitative data in form
of CT no. (electron density) for
tissue heterogeneity corrections
CT
IMAGING

38. CT localizer
• A CT indicator box has a Z-shaped fiducial (F) frame
embedded within each panel. The fiducial frames are
manufactured from a high contrast copper material.
The coordinates provided by the fiducials can be determined manually or
automatically by the treatment planning application. This is known as defining
the images.

40. MR localizer
• The design of an MR Indicator box is different from
that of a CT indicator box to accommodate the
requirements of the imaging process. In MR Indicator
boxes the fiducials (F) consist of a Z-shaped cavity
filled with copper sulfate.

42. • Requires MRI compatible
localization box.
• scans directly in axial,
sagittal, coronal or oblique
planes
• Better imaging of soft
tissue tumors.
• Can assess neural invasion
MRI

43. • PET detects early stage tumors which CT & other
imaging modalities may miss & provides functional
information
• Positron emitting radionuclide, produced by
bombardment of stable nuclide with proton from a
cyclotron, are attached to biological markers
• Most commonly used biological marker in cancer
diagnosis is - 18F radionuclide attached to 2-fluoro-2
deoxy-D-glucose (FDG).
• Cancer cells metabolize radiolabelled glucose at
much higher rate than normal cells.
PET

44. • PET detects photons liberated at 180° by annihilation reaction of
positron with electron
• simultaneous detection of this pair and subsequent mapping of
the event of origin allows spatial localization
• The detectors / scintillators (BGO) are arranged in an circular
array around the patient & convert γ - energy into visible photons
detected by PMTs
• Disadv. Of PET
o poor resolution
o can not pinpoint exact size & location of tumors to the
precision required for optimal diagnosis & treatment planning
o Separate PET & CT images are difficult to fuse
PET

45. PET/CT

46. • Important for AVMs
• Angiographic
localizer is attached
to BRW head ring.
• Consists of four
plates embedded with
four lead markers
which act as fiducial
markers for angio
graphic images
ANGIOGRAPHY

47. Angio localizer
. They are particularly useful for visualizing the
arteriovenous malformation within the brain.
Angiographic images are also acquired by using Leksell®
Coordinate Frame with a special AI indicator attached.
The fiducials are made of high-density material that is
clearly visible on angiograms. Each plate has four
fiducials shaped as either crosses or plus signs.

48. • Employs a unique algorithm that allows for full voxel to voxel
intensity match, Image Fusion automatically correlates thousands
of points from two image sets, providing true volumetric fusion of
anatomical data sets.
• Advantages
o Reuse of costly scans
o Fusing CT & MR image combines spatial accuracy of CT with
the superior tissue definition of MR thus improves the
accuracy of using certain types of scans for stereotaxy.
o Ability to fuse non-localized images into stereo tactic space
o Fast volumetric matching of two image sets
o The ability to align pre- and post-operative scanned images
with Image Fusion™ improves follow-up evaluation.
IMAGE FUSION

49. Steps of gamma knife
planning
• Acquired images transferred to TPS
• Co-ordinates of target are recognized by computer
with help of fiducials
• Target volume defined by drawing margin to lesion
• OAR outlined
• Dose level that would ideally cover entire target
volume selected
• Maximum dose to tumor is set
• Target volume is covered with shots, each application
of radiation is referred to as shot
• Shot produces isocenter that can be defined as
active radiation field

50. • No: of shots required to deliver dose to entire tumor
volume is determined by size, geometry & location of
tumor volume
• Usually more than one shot/isocenter is required to
treat a tumor because of smaller field size & fixed
beam geometry
• Optimization of parameters : number of shots, shot
sizes, shot location, shot weight, collimator helmet,
plugging pattern

52. • The intensity of each shot & its weight depends on
how long the involved collimator remains open
• Shot position defined relative to stereotactic frame
by x, y & z co-ordinate position so that target is
precisely at the isocenter of collimator helmet
• Once the treatment plan is completed, plan is
exported via network to console computer

54. Plan evaluation
• Technique of plan evaluation
 Display of isodose lines over target volume
 Display of 3D dose shell
 Display of DVHs

55. The accuracy of the Gamma Knife is demonstrated, by showing the beam
profile. Here we see, that even millimeters away from the center of the target
(which receives a great deal of radiation), the brain tissue receives minimal amounts
of radiation. This is very important for protection of the normal brain tissue which
may surround a brain tumor.

56. EXECUTION (GAMMA
KNIFE)
• Pt. lies down on sliding
couch of gamma unit
• Head frame is
attached to
appropriate helmet
• Couch moves either
electrical mechanism or
hydraulic system
• & helmet docks in to
beam channels.
• After treatment, head
ring removed & patient
discharged the same
day

57. CONTROL CONSOLE

58. Evolution of
gamma knife over
time

59. Treatment machine -
models
• There are five current version of Lekshell gamma
knife
 U
 B
 C
 4C
 Perfexion
 Icon

60. Gamma Knife prototype
• 179 C0-60 source
• Elliptical collimator
• Designed for functional
disorder
• First treatment in 1968

61. Model U
• Introduced by Elekta in 1987
• 201 C0- 60 source with 4, 8,
14, 18 mm helmet
• Manual setting of coordinates
• Difficult to load at apex

62. Model B
• 201- CO-60 sources
• Annular geometry
• Easier to load and reload
• Manual loading

63. Model C
• Dedicated unit with automatic
positioning system
• Computer controlled setting of
coordinates eliminates human error
• Fast treatment delivery
• Lower radiation dose to extra
cranial compartment
• Lower radiation dose to operator
• Introduced in 1999

64. • Model 4C :
introduced in 2005
with integrated imaging capabilities
• PERFEXION :
introduced in 2006
with larger aperture
internal secondary collimator
can treat cervical spinal lesion also

67. GAMMA KNIFE PERFEXION
• Major redesign of the Gamma Knife.
• July 2006 – 1st system became operational at Timone
University Hospital of Marseille France. • August 2006
- FDA approval

68. • The Gamma Knife Perfexion includes a variety of
enhancements including
• • Internal collimation: The Perfexion includes an
internal collimation system. Rather than being fixed,
the cobalt sources are grouped into 8 sectors. Each
position corresponds to a different size collimator
(4mm, 8mm, 16mm or blocked)

69. • • Composite isocenters: Because each of the 8
sectors of sources can move independently, it is now
possible to create composite shots where each sector
is of different collimator size (for example, part
4mm, part 16mm, part blocked).

70. • • Automated shielding: With the Perfexion unit,
there is no more requirement for manual plugging of
collimator helmets. Because one of the source
positions is a blocked position, plugging becomes an
automated process.

71. • • Simplified patient fixation: A special adapter is
attached to the head frame, and this adapter fits
simply into a head holder attached to the bed. The
weight of the patient’s head can be supported at all
times by the bed.

72. • • Improved patient comfort: The entire bed of the
Perfexion moves from position to position (rather
than just the head), the relative position of the
patient’s head and neck does not change during the
treatment. These two changes promise to
significantly improve patient comfort.

73. Beam Collimation
• The most critical change in the perfexion is the new
collimator system .
• The new system replaces the multi-helmet collimator
setup with a single integrated permanent collimator
system that incorporates openings for 4mm,8mm and
16mm treatment beams .
• The collimator is partitioned into 8 independently
moveable sectors each delivering 24 beams of
radiation (192) total sources.
• Beam size can be changed dynamically by sector
• Individual sectors can be blocked to provide further
shaping of each shot of radiation.

74. POSITIONING SYSTEM
DESIGN
• The GK Perfexion model positions the patient by
moving the couch rather than moving the patient’s
head within an APS.
• The transition between shot locations is typically 3
seconds.

75. ICON Elekta
• Leksell Gamma Knife Icon gives the option to
perform single or fractionated frame-based or
frameless treatments, allowing for more
individualized delivery—without sacrificing precision
and accuracy.

76. • Unique Features
• Fully integrated, non-complex system design
• Automatic delivery correction and dose evaluation
• 2-4 times lower dose to healthy brain

77. • Essential Features
• Quick QA procedure (maximum 10 minute daily)
• Fast and intuitive dose planning
• No need for margins
• Planned dose equals delivered dose with guaranteed
system accuracy over lifetime of device
• Evidence based performance

78. • Flexible and intuitive workflows
• Well-defined workflows enable fast and intuitive dose
planning, even for complex cases
• Operational efficiency
• Fully automated treatment delivery allows for small
teams and high throughput regardless of treatment
volume

79. QUALITY ASSURANCE IN
RADIOSURGERY
• Q.A. protocol for radio surgery falls into three
categories
o Basic quality assurance for all equipment used for
target localization,3-D treatment planning & radio
surgical dose delivery
o Treatment quality assurance protocol dealing with
calibration & preparation of equipment just before
radio surgical treatment
o Treatment quality assurance during radio surgical
procedure on patient

80. Timer Test
Timer is tested for :
Linearity
Constancy
Accuracy
Checked over range of time
in clinical use : < 1 – 60 min
A special spherical phantom
with 80 mm radius is used
for all dosimetric
measurements
Has slots for other measurement
methods too
Dosimeter : 0.07 cc
ionization chamber
All measurements made with
18 mm helmet with all
collimators open

81. Output Factors
Same setup is used.
The ionization chamber is calibrated against
a standard ionization chamber which
measures the dose in a 5x5 cm cobalt field
in the same phantom (80 mm depth)
The dose output is referred to as dose to
water.
The dose output is then corrected based on
decay corrections
Monthly checks for output should have
variation ± 3%

82. Isocenter coincidence
Check is done for the
coincidence between the
radiation and mechanical
Isocenter
A special aluminum film container is
used
Irradiation is done with the 8 mm
helmet in axial and coronal positions
Radiation isocenter – half
of width at half maximum
Mechanical isocenter –
indentation in the film
Desired value ± 0. 3 mm
(RMS of all three axes)
Width at half
maximum

83. Mechanical Accuracy
Another test is a lead
shot test
Uses a 20 cm diameter
phantom
A 4 mm lead shot is
placed in the center
Film strips are pasted
over the phantom
Beam is turned on and
the films developed
N.B. Lead shots are
placed in the center of
the exits of Co60 beam
from each aperture

84. Dose Profile Check
The dose profile check allows comparison of accuracy
of the alignment between the primary collimator and
the helmet.
A film is placed in the center of the spherical
phantom and irradiated
The film is scanned and compared against the
previous film record to see any minute misalignment
The test is repeated annually and with all four
helmets

85. Couch movement Speed
The time of the movement of the couch is set to
minimum to minimize unnecessary radiation exposure
for the patient.
Checking is done monthly
Transit time deviation includes time for entry as well
as exit
It should be of the order of < ± 30 sec

86. Model 4c or earlier

87. Emergency procedures of
gamma knife
• In case of emergency situation in which there is a risk of injury to the
patient or operator, emergency procedures must be followed.
• The goal of the emergency procedures is to take the patient and the
system to a safe state
• i.e.
• The patient is taken out of the radiation unit
• The shielding doors are closed and the sectors are locked in the sector
home position (beam off)
the following procedures are available in an emergency situation
• Treatment pause (to initiate an out transport of the patient )
• Emergency stop (to immediately stop all movements )
• Manual pull-out of the couch (if the couch did not return)
• Emergency undocking(if the couch cannot be pulled out )
If contact with the collimator cap has occurred , a manual pull-out of the couch is required

88. Emergency stop
• The emergency stop button is located in the upper right corner of the
control panel .optionally , local regulatuions may require other
emergency stop buttons to be installed in the treatment room or
elsewhere in the control area .
• To activate an emergency stop, press the emergency stop button .
When the emergency stop is activated :
• The couch and shielding doors stop and hold their position,
• The sectors return to the sector home position
• An error message is displayed in the system information area of the
treatment monitor .
Resetting the emergency stop will initiate the emergency exit sequence :
• The couch returns to the home position,
• The shielding doors close.
To reset the emergency stop button , turn it counter clockwise as
indicated by the arrows on the button .

89. Manual pull out of the
couch
• If the couch has not returned from the treatment position , the patient must be
withdrawn from the radiation unit by pulling out the couch by hand .
ACTIONS
• If the contact with the collimator cap has occurred ,pull the couch release
handle for X movement. Pull or push the couch slightly towards the center
position.
• Pull the couch release handle for Z movement. Pull the couch out to the fully
withdrawn position .
• Release the patient from the couch . Leave the treatment room together with
the patient.
AFTER THE PATIENT IS SAFE
• Push back the couch release handles into locking position.
• In the control room, acknowledge the error and let the system initialize.
• If the shielding doors did not close during the initialization sequence , manually
close the doors
• If the sectors have not returned to their home position, manually close the
sectors

90. ADVANTAGES
• Precision
• Safety
• Effective
• Technologically advanced

91. Disadvantages of gamma
knife
• Limited application
only in intracranial tumors, upper cervical
central lesions
small sized tumors
• Multiple radioactive source
issues concerning radiation protection
source replacement

92. X-Knife
• LINAC-based systems (X-Knife)
– High-energy x-ray from linear accelerator
device
– Can use fractionation

93. X-Knife……
• Radio surgery system which
includes stereotactic
accessories along with LINAC
Working principle: High energy
X-rays similar to LINAC
Source: Conventional LINAC of
high energy 6-18 MeV
• Collimator system: Cone
based
mMLC based

94. CONE BASED
 Highly collimated narrow beams
defined by
 15cm long circular cones made of
Cerrobend Lead, encased in
stainless steel.
 The cones are mounted below X-
ray jaws
 A range of cones with dia. from
5mm to 40mm in steps of 2.5mm
are used for SRS lesions
 A few cones of larger dia. are
also available for treating larger
lesions with SRT

95. MICRO MLC BASED
 used for small irregular field SRS/SRT
 for greater conformity & efficiency
than circular collimators
 Simple mounting & dismounting
 Computer controlled motorized leaves
 Number of Leaves : 52 (26 pair)
 Field Size (max): 10 cm x 10 cm
 Leaf Width : 2.5 mm at isocenter
 Leaf Height: 7 cm
 Leakage (through Leaf):<1%
 Leakage (Interleaf)
 Avg. 1.2%,
 Max. 2.0%Maximum
 Leaf Speed:2.5 cm/sec

96. TOOLS FOR SRS/SRT X- KNIFE BASED
 CT localizer
 MR localizer
 Angio localizer
 Fixation Frame
 BRW frame (SRS)
 GTC frame (SRT)
 Depth Helmet
 LCMA (Linac couch mount assembly)
 RLPP (Rectilinear Phantom Pointer)
 LTLF (Laser Target Localizer Frame)

97. TOOLS FOR SRS/SRT
LCMA
RLPP
LTLF
DEPTH
HELM
RT

98. • Images are transferred to 3-D planning system
• Image fusion is done for better delineation of target
vol.
• Target volume & Organs at risk delineated on scans
• X, Y, Z coordinates of patient on the image are
determined with accuracy of +/- 1mm
• Dose plan is created on target vol. setting dose limits
TREATMENT PLANNING (X-
KNIFE)

99. TREATMENT PLANNING (X-KNIFE)
• To achieve steep dose gradient i.e.
instantaneous decrease from target dose to
zero dose over no distance non coplanar
multiarc technique is used in linac radio surgery
• Optimization parameters are
o Isocenter position
o no. of arc,
o arcing angles
o arc wt. &
o couch angles.
• Couch angles are specified w.r.t. gantry
angles

100. Head frame
• Light wt aluminum box shaped head
frame defines fixed coordinate system
for accurate localization & irradn of PTV
• The head frame serves following
purposes:
o It enables accurate reproducibility of the treatment
position for each planning and treatment session.
o It prevents movement of pt.’s head during the treatment

101. QUALITY
ASSURANCE

102. • Verification components
 LTLF (LASER Target
Localizer Frame): for
precise positioning of target
at beam isocentre
 RLPP (Rectilinear LINAC
Phantom Pointer)
LTLF

103. • Target vol.
Coordinates set on
RLPP as obtained
from 3-D TPS
• Attach LTP to RLPP
• Laser alignment
checked on LTP in lat.
& vertical direction
by adjusting couch
• Set same coordinates
on LTLF & attach it
to RLPP & lock the
system
• All lasers should pass
through respective
cross hair with an
accuracy of <0.5mm

104. • LTLF is removed & a
film holder is
attached to
collimator assembly
• Exposuers are given
with diff. gantry
angles & couch fixed
& vice versa
• Centre of radiopaque
ball & radn fields are
marked by suitable
concentric circular
template
• Distance b/w two
centers found by
calibrated
microscope it should
not be >0.5mm

106. TREATMENT Q.A.
• RLPP & LTLF are taken out
• Pt lies on the couch with BRW/GTC frame
fixed to his head & LCMA
• LTLF again attached & couch raised so that all
lasers coincide
• Before starting the treatment gantry is
rotated from starting angle to end of arc with
couch at angle obtained from TPS to ensure
that there is no collision

107. X-knife
Advantages
• Permits fractionation
• Variety of beam shaping techniques available i.e. treatment
of irregular targets
• Flexibility in selecting field size
• Permits intensity modulation of beams
• Much lower installation cost
• Can be used for other routine treatments
Disadvantages
• Accuracy for small targets is questionable
• Less accurate, longer treatment time
• Frame based targeting only for brain lesions

108. XKNIFE γ knife
system Can be used for conventional
RT
Dedicated for SRS(
intracranial)
source Tungsten target Co-60
Radiation X-rays produced when high
speed e- strike target
γ radiation produced by
radioactive decay of Co-60
optimization Achieved by varying arc angle,
arc weights, couch angle etc.
Achieved by plugging holes of
collimator helmet
cost 1/10th of cost of γ knife expensive
Field Size Max. available 4cm Max available 1.8cm

109. X KNIFE GAMMA KNIFE
Tumor size Used for larger lesions Can be used for small lesions
because of FS limitation (max.
dia.18mm)
isocenter Multiple isocenters lead to
dose
heterogeneity within TV
Multiple isocenters can be placed
to expand dose distribution
Dose
distribution
Dynamic MLC required to
produce conformal
distribution
Produces more conformal dose
distribution
Prescriptio
n
90% isodose 50% isodose
Beam
geometry
not fixed Fixed

110. • Industrial robot arm with
6MV linac
• Image guidance system -
two orthogonal ceiling
mounted X-ray camera
with floor mounted flat
panel detector
o Continuously monitors &
corrects for changes in pt.
position & motion
• Extra cranial capability.
CYBER KNIFE
X-ray camera
A - Si
detectors
Treatment
couch
Robotic arm
linac
Accuracy cyber knife

111. • The principle involved is similar to that used
in guiding cruise missiles.
• Detectors are linked to an image
registration computer.
• Pretreatment CT based DRR’s are compared
to digital radiograph acquired, using
radiographic land marks
• Data is then transferred to the computer
controlled robot & adjust the position of
robotic arm accordingly
• assuring that beam points at the intended
location within the patient with millimeter
accuracy.
• Six axes of robotic arm motion provide
unparalleled beam directionality for optimum
dose conformity, especially for complex
lesion shapes.
HOW IT WORKS?

112. • Aims to dispense with
invasiveness of stereo tactic
frames without losing
inherent accuracy of frame
based approach
• Image guidance is used. Based
either on
o surgical implantation of fiducial
markers ( gold seeds, wires &
screws.
o Or on-line planar imaging
FRAMELESS
STEREOTAXY
Bio-compatible Gold Markers

113. • used for tumors that are in continuous motion while being treated e.g.
lung & pancreatic tumors
• using x-ray cameras to continuously image its location would require
large amount of radn to patient’s skin.
• uses a combination of surgically placed internal fiducials, and light
emitting optical fibers ( external markers) usually placed on the
patient abdomen, so that their motion reflects the internal motion of
the diaphragm, and the lungs.
• The light from the markers is tracked continuously using a CCD
camera
• The system take images of the internal fiducials, and predict their
location at a future time using the motion of the markers that are
located on the patients skin.
• Their motion is correlated with the motion of the tumor.
• A computer algorithm creates a correlation model that represents
how the internal fiducial markers are moving compared to the external
markers.
SYNCHRONY
SYSTEM

114. o Allows frameless radio surgery
o Monitors & tracks the pts. position during treatment
o Achieves a dose delivery accuracy of the order of
1mm through image guided dose delivery method.
o Allows for frameless radio surgical dose delivery to
extra cranial lesions such as spine, lung & prostrate.
o Large no. of beam angles are available.
o There is animated visualisation of whole plan before
actual execution of treatment plan.
ADV. OF CYBER KNIFE

115. • No posterior (below couch) possible.
• Prolonged treatment planning time.
• Long treatment time.
• Significant QA required prior to treatment to ensure
that robotic arm performs as expected.
DISADV. OF CYBER
KNIFE