Detailed description of Stereotactic Radiotherapy/ Radiosurgery

1. Dr Umesh V

2.  Stereotactic radiotherapy dates back more than 50 years;
however, this form of treatment has entered the domain of
radiation oncology only in the past 10–15 years
 Stereotaxy (stereo + taxis – Greek, orientation in space)
is a method which defines a point in the patient’s body by
using an external three-dimensional coordinate system
which is rigidly attached to the patient.
 This results in a highly precise delivery of the radiation dose
to an exactly defined target (tumor) volume.

3. Stereotactic Radiotherapy
The delivery of multiple fractionated doses of radiation to a
definitive target volume sparing normal structure (both intra
as well as extracranial)
Stereotactic Radiosurgery
The delivery of a single, high dose of irradiation to a small and
critically located intracranial volume, sparing normal
structure
 The aim is to encompass the target volume in the high dose
area and, by means of a steep dose gradient, to spare the
surrounding normal tissue

4.  The intention of SRS is to produce enough cell kill within the
target volume in a single fraction in order to eradicate the
tumor.
 This single high irradiation dose can produce considerable
side effects in normal tissue located close to the tumor or
within the target volume.
 The SRT combines the precision of target localization and
dose application of SRS with the radiobiological advantage of
fractionated radiotherapy, i.e., breaking the total dose into
smaller parts and thus allowing repair of DNA damage in
normal tissue during the time between fractions.
 Time intervals of more than 6 h between fractions can
significantly reduce the risk of side effects in normal tissue

6. Conventional
Stereotactic
coplanar setup
non-coplanar setup
large volumes
small volumes
less no. of fields
more no. of fields
target volume delineation
precise delineation
positional accuracy ± 5 mm
positional accuracy ± 1 mm
Optical field, SSD indicator
Target volumes precisely
delineated
Marking on patient.s skin
Margins not necessary
Normal cells within the target
negligible

7.  The first one to combine stereotactic
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methodology with radiation therapy
was the Swedish neurosurgeon Lars
Leksell. Leksel performed the first
treatment in 1951, at the Karolinska
Institute, and called the new therapy
approach radiosurgery (RS)
Leksel continued his work and built
the first isotope radiation machine, in
1968, the Gamma knife
The stereotactic radiation therapy
with LINAC started in the early 1980s:
the Swedish physicist Larsson
proposed to use the LINAC instead Co
60 or protons (Larsson et al. 1974)
The first published reports on clinical
use of LINAC came from Buenos Aires
and Vicenza
In India AIIMS started SRS/SRT on
27th May 1997

9.  The stereotactic coordinates are a cartesian three-
dimensional coordinates system attached to the stereotactic
frame in a rigid relationship.
 The origin of the stereotactic coordinates system is generally
in the center of the volume defined by the stereotactic frame:
 The x and y axes correspond to the lateral and frontal side of
the frame and the z axis to the cranio-caudal direction

10.  The main steps in the planning and delivering of stereotactic
irradiation treatment are:
1. Rigid application of the stereotactic frame to the patient
2. Imaging (CT, MRI, angiography) of the patient with the frame
and localizer attached to the frame
3. Treatment planning
4. Positioning of the patient for the stereotactic radiation
therapy
5. Delivery of the irradiation
6. Quality assurance

11.  Stereotactic radiotherapy is based on the rigid connection of
the stereotactic frame to the patient during CT, MRI, and
angiography imaging
 The stereotactic frame is the base for the fixation of the other
stereotactic elements (localizer and positioner) and for the
definition of the origin (point 0) of the stereotactic
coordinates.
 During the whole treatment procedure, from the
performance of the stereotactic imaging to the delivery of the
irradiation treatment, the stereotactic frame must not be
removed from the patient.
 In case of relocatable frames it must be assured that the
position of the patient is exactly the same relative to the
frame after reapplication of the relocatable frame

12.  For the treatment of cranial
lesions by RS the frame
system is neurosurgically
fixed onto the patient’s skull
 For SFR the head is fixed
non-invasively in a
relocatable thermoplastic
mask attached on the
stereotactic frame

13.  There are different stereotactic frame systems
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described in detail in the literature:
the BRW system
the CRW system
the Leksell system
the BrainLAB system
Each system is different with regard to
material of the stereotactic frame, design, and
connection with the localizer and positioner
and accuracy of repositioning

14.  Imaging is used in stereotactic radiotherapy for:
(a) Localization and positioning;
(b) Definition of target volume and organs at risk; and
(c) Calculation and 3D representation of the isodose
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distribution
MRI describes the anatomical structures of soft tissue with a
high accuracy
CT is important for the delineation of bone and soft tissue
Positron emission tomography (PET) and single photon
computed emission tomography (SPECT) offer additional
information about tumor extension and biology
Angiography is essential for the visualization of the arteriovenous malformations

16.  Most stereotactic systems use CT for localization
 During the CT investigation the localizer is attached to the frame
 The localizer is a box with CT-compatible fiducial markers on each
plane, which are visualized on CT on each scan; thus, the localizer
defines the link between the stereotactic coordinates and the imaging
coordinates, so that for any point in the imaging the 3D stereotactic
coordinates can be determined.
 The stereotactic frame, the patient fixation system, and the localizer
form a fix unit.

17.  Definition of Target Volume and Organs
at Risk
 Definition of the Stereotactic Target
Point
 Planning of the Radiation Technique
 3D Dose Calculation
 Dose Specification
 Visualization of the Dose Distribution

18.  The tumor-specific morphology, the growth pattern of the
tumor, and the anatomical relationship to the normal tissue
are essential parameters in defining the target volume.
 Of major importance for the stereotactic radiation therapy is
the delineation of the organs at risk.
 All the organs at risk which may get significant dose have to
be delineated

19.  The target point is the point in the target volume that must be
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positioned with exact precision in the isocenter of the LINAC.
The position of the target point can be defined interactively.
One or more target points can be defined.
In stereotactic planning programs the coordinates of the target
points are related in such way that the resulting dose distribution
meets the clinical requirements.
The planning system outputs the position of these points in
stereotactic coordinate.
Prior to therapy, these coordinates will be used to correctly
position the patient.
This is performed with a positioner, a device attached to the
stereotactic frame, which allows the connection of the stereotactic
coordinate system to the room coordinate system, where the
isocenter of the treatment device is defined

21.  The following parameters can be defined interactively in the
process of radiation planning:
 the number and position of the target points;
 the number of the radiation arcs and static fields and
their shape;
 the position of the gantry and radiation table; and
 the radiation dose in the target point for each field or
arc.
By combining these parameters the radiation plan is
developed.

22.  The stereotactic radiation is characterized by a very steep
dose fall-off on the margin of the target volume.
 The steep dose gradient is achieved by the use of appropriate
collimators and a multitude of radiation directions.
 Stereotactic Collimators. Tertiary stereotactic collimators
for circular or oval target volumes are attached to the tray
holder of the LINAC. The diameter of the irradiated area is
defined by the size of the circular collimators and varies
usually between 1 and 35 mm

23.  Micro-multileaf collimators have recently become available . The
beam shape can be selected by computer or by hand. In this way the
contours of the irradiation field can be adjusted individually to the
tumor shape. Micro-multileaf collimators, in comparison with the
traditional multi-leaf collimators, have the advantage of a decreased leaf
width and therefore optimized the resolution (between 1 and 3 mm).

24.  Convergent Radiation Techniques. The radiation techniques are
in general isocentric and implemented by using a rotational
technique (using circular collimators or dynamic fields) or a
static-field technique; both can be combined with an isocentric
table rotation.
 In the rotational technique usually five to ten radiation arcs are
used.
 The size and the angle between the arcs are variable and are
responsible for the conformal isodose distribution.
 The stereotactic irradiation with the micro-multileaf collimator is
done with multiple static irradiation fields (usually 6–12 fields)

26.  Most of the planning systems use CT images for the calculation of the
correct dose.
 The planning software converts the Hounsfield number of the CT data
into an electron density.
 Some planning software programs use MRI information only, by
considering homogenous soft tissue density for the calculation of the
dose.
 Stereotactic radiation therapy can use simple dose-calculation
algorithms because no large-density inhomogeneities are in the brain.

27.  The prescribed dose, Do, is the isodose surface which is
intended to completely encompass the PTV.
 The minimal dose, Dmin, and the maximal dose, Dmax, in
the PTV have to be specified as well.
 In the radiation plan, based on ICRU 50, different volumes
have to be considered as well: PTV, treated volume, as well as
the percentage of the target volume which will be irradiated
with a dose higher than Do.
 The maximal dose in the area of risk structures has to be
defined as well.

28.  The decision for the best
radiation plan is made after
evaluation of the dose
distribution based on the
isodose curves dose volume
histograms, conformity index,
or mathematical models for
the normal tissue complication
probability and tumor control
probability, similar to the
conventional 3D radiation.
 The definitive decision for the
best treatment plan must be
made by the physician, using
clinical judgment, after the
rigorous evaluation of the dose
distribution in the complete
3D data base.

29.  The positioning of the patient
on the LINAC is done by using a
stereotactic positioner .
 This instrument allows to
project the coordinates of the
target point onto orthogonal
planes attached to the
stereotactic frame.
 By the use of this projected
target point, the patient can be
positioned in a way that the
target point and the isocenter of
the LINAC overlap exactly.
 The position of the isocenter
is indicated by a room-based
laser positioning system

30.  After positioning the patient, the target
instrument (positioner) is removed and
the radiation can start.
 The most important requirement for the
use of the isocentric LINAC for RS and
stereotactic radiation therapy is the
accuracy of the isocenter: under ideal
conditions the axis of the gantry
rotation, the central axis of the beams
and the rotation axis of the rotation
table convert in one point, the isocenter
 In general, it is acceptable that the three
axes – gantry rotation axis, central axis,
and table rotation axis – meet in a
sphere which coincides with the
isocenter and has a diameter of
approximately 1 mm.
 They must be constantly controlled
during regular quality-control
procedures.

31.  The essential requirement for the clinical use of the LINAC is
quality control based on well-defined protocols
 The quality-assurance protocols address the precision of the target
volume and target point with CT, MRI, PET and angiography, the
dosimetry, the planning of the irradiation, and especially with the
calibration of the absolute dose and of the dose application.
 For the quality-assurance assessment proper phantoms and
specialized dosimetric instruments must be available.

32.  Tumor volume — As the size of the target lesion for SRS
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increases, incidental irradiation to the surrounding normal tissue
also increases. This may be important since a much higher dose of
irradiation is administered with SRS compared to fractionated RT.
SRS was not recommended for lesions >4 cm because adequate
control could not be achieved without an unacceptable level of
radiation toxicity to surrounding normal tissue.
Proximity to cranial nerves — The proximity of a target to
cranial nerves can cause radiation neurotoxicity, despite the steep
decrease in dose outside the intended target Fractionated RT
should be considered when SRS may jeopardize cranial nerve
function.
Cranial nerves II and VIII are more sensitive to radiation injury
than the other cranial nerves. SRS is generally avoided if the
maximal dose delivered to the optic nerve exceeds 10 Gy.
Location of the lesion — The risk of developing permanent
damage following SRS varies dramatically with the location of the
lesion in the brain. Fractionated RT is often preferred to SRS for
the treatment of lesions in the deep gray matter or the brainstem

33. • Enhances clinical outcome
• Improves quality of life
• Time factor

34.  Clinical Outcome-Documented scientific data shows better
or equal results compared with microsurgery, Fewer
complications, Reproducible results ,Treatment solution for
inoperable patients, Combined treatment with microsurgery
and endovascular techniques extend the capabilities
 Quality Of Life- Minimally invasive, Less trauma, Faster
recovery, Minimal hospitalization, Fewer complications ,
Documented efficacy
 Time Factor

35. High cost of purchase and use
Risk of neurological injury
Risk of mechanical inaccuracy
Potential necessity of multiple
visits

36. Malignant
 Meningioma
 Pituitary tumors
 Acoustic neuromas
 Metastatic brain lesions
 Glioma
 Vascular
AVM
 Functional
Trigeminal Neuralgia
 Research Areas
. Movement Disorders
. Intractable Pain
. Epilepsy
. Macular Degeneration
. Uveal Melanoma

37. Dose plan with 6 isocenters
- Minimizing dose to optic chiasm

39. Pre treatment
54 months post

40. Pre treatment
Pre treatment
2 months post treatment
10 months post treatment

42. Pre Gamma Knife Surgery

43. 2 years post Gamma Knife Surgery

44. Pre treatment
Dose Plan
13 Months Post treatment

47.  Gamma Knife Radiotherapy
 Rotating Gamma System(RGS)
 Proton Radiosurgery
 LINAC Radiosurgery
 Tomotherapy
 LINAC Image guided Radiotherapy

48.  Gamma Knife- In 1999, the model C
version of the gamma knife was
introduced with the option to use
robotic positioning to set treatment
coordinates. This expedites execution
of multiple-isocenter treatment plans.
The model 4-C, introduced in 2005,
was equipped with enhancements
designed to improve workflow,
increase accuracy, and provide
integrated imaging capabilities. The
Perfexion model introduced in 2006
uses a larger patient aperture and
internally mounted secondary
collimators
 RGS-A radiosurgery device called
the rotating gamma system (RGS)
was developed in China. The rotating
gamma system employs 30 cobalt-60
radiation sources in a revolving
hemispherical shell. The secondary
collimator is a coaxial hemispheric
shell with six groups of five different
collimators to produce spherical
treatment volumes of different
diameter

49.  Proton Radiosurgery
 The chief advantage of charged proton
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radiosurgery is that the beams stop at
a depth related to the beam's energy.
The lack of an exit dose and the sharp
beam profile of protons allow target
irradiation with lower integral doses
than are delivered with photon (Linac
x-ray or cobalt-60 gamma) irradiation.
An unmodified proton beam
irradiation deposits increased energy
in the last couple of millimeters of the
path length.
This area of increased ionization,
where cell killing is even higher
because of an increased radiobiologic
effect, is termed the Bragg peak or
Bragg-Gray peak
The first treatment of a malignant
tumor by irradiation with a proton
beam Bragg peak was carried out in
1957 and followed by functional
neurosurgery for advanced
Parkinson's disease in 1958.

50.  LINAC Radiosurgery
 Many LINAC-based systems
such as Xknife, Novalis, the
Peacock System, and
Cyberknife are commercially
available
 The Cyberknife combines a
miniaturized LINAC mounted
on an industrial robot with a
system for target tracking and
beam realignment
 Cyberknife plans use multiple
fixed-beam positions and
multiple isocenters.
 Before the radiation is
delivered from any beam
position, the target position is
tracked using an integrated xray image processing system,
consisting of two orthogonal
diagnostic x-ray cameras and an
optical tracking system.

51.  Tomotherapy rapidly rotates the beam around the patient
(and inside the housing of the unit), thus allowing the beam
to enter the patient from many different angles in succession

52.  The combination of the stereotactic radiation therapy of the
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LINAC with IMRT opens new perspectives for those entities
where exact conformal and high doses must be delivered
The first analysis of RS with dynamic field shaping technique
in comparison with conformal static beams and multi-isocentric
non-coplanar circular arcs showed that the dynamic-arc
technique combines simple planning, short treatment times,
dose homogeneity within the target, and rapid dose falloff in
normal tissue
A new method under development is robot-assisted RS. The
LINAC in this device is mounted on a robotic arm with 6 degrees
of freedom
In past years progress has been made in the field of frameless
stereotactic radiation therapy.
For neuronavigation internal and external markers are used
for positioning the patient with stereoscopic video cameras
and X-ray machines

53.  AIIMS, New Delhi
 Apollo Hospitals India
 Yashoda Hospital Hyderabad
 HCG group of hospitals Bangalore
 Adyar Cancer Institute
 Dharamshila Hospital Delhi
And many more.

55. Lars Leksell.