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
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 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
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 arterio-
venous 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
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
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
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
38. 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
39. Proton Radiosurgery
The chief advantage of charged
proton 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
40. 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
x-ray image processing
system, consisting of two
41. 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
42. The combination of the stereotactic radiation therapy of
the 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
43. AIIMS, New Delhi
Apollo Hospitals India
Yashoda Hospital Hyderabad
HCG group of hospitals Bangalore
Adyar Cancer Institute
Dharamshila Hospital Delhi
And many more.