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1. AMRITA INSTITUTE OF MEDICAL SCIENCES –KOCHI (INDIA)
SRS AND SRT
Arun Adhikari
PGDMRS -21
Date - 29 September 2022

2. Overview
Introduction
Conventional and Stereotactic comparison
Advantages
Treatment of Diseases.
Treatment techniques and units
X ray knife
Stereotactic frame
Gamma Knife
Cyber-knife
Proton Therapy
Dosimetry
Quality Assurance
Side Effect
Conclusion
References

3. Introduction
Stereotactic - Stereo + Taxis = Orientation in Space
This means Three Dimensional localization of a point in space by a unique set of coordinates that
relate to a fixed, external reference frame.
SRT- The delivery of multiple fractionated doses of radiation to a definitive target volume sparing
normal structure.
SRS- The delivery of a single, high dose of irradiation to a small and critically located volume,
sparing normal structure. It is limited to lesions that are well defined and not larger than 3-4 cm
These techniques involves 3 Dimensions imaging to localize the lesion and delivering treatment.
Small field used in SRS/SRT is generally defined as having dimensions smaller than lateral range of
the charged particle that contributed to the dose deposited at a point along central axis

4. According to this criteria small field size for 6MV photon should be less than 3
×3cm2.
Hallmarks of SRS/SRT
 High degree dose
 Accuracy
• These are obtained using specially designed stereotactic apparatus
• Apparatus is used in all steps of process ; Imaging, Target localization, Head
immobilization and Treatment setup.

5. Conventional and stereotactic
Conventional
 Coplanar setup
 Large volumes
 Less no. of fields
 Target volume delineation
 Positional accuracy ± 5
mm
 Optical field, SSD
indicator
 Marking on patient’s skin
(thermoplastic sheet)
Stereotactic
 Non-coplanar setup
 Small volumes
 More no. of fields
 Precise delineation
 Positional accuracy ± 1 mm
 Target volumes precisely
delineated
 Margins not necessary
 Normal cells within the target
negligible

6. Advantages
Quality of life
 Minimally invasive
 Less trauma
 Faster recovery
 Minimal hospitalization
 Fewer complications
 Documented efficacy
Clinical outcome
 Better or equal results
compared with microsurgery
 Fewer complications
 Reproducible results
 Treatment solution for
inoperable patients
Time Factor
DIAGNOSIS
GAMMA
KNIFE
SURGERY
OPEN
SURGERY
2-4 DAYS ICU
10-20 DAYS
HOSPITALIZATI
ON
4-6 WEEKS
CONVALESCENC
E

7. Treatment
AVM Acoustic Neuroma
2 years post
Pre 6 months post

8. Meningioma (Dose plan with 6 isocenter) After 2 years

9. Astrocytoma
Pre 5 years post

10. .
Trigeminal Neuralgia
Dose plan 6 months post

11. Treatment techniques and units
 Charged particle beams - Proton Beam Therapy
 Gamma ray photons - Gamma Knife ,RGS
 X-ray photons - Modified & dedicated Linac (X-Knife), Cyber-
knife
 Neutrons have been unsuccessfully
Most of the Radiation Generators used for SRS are also used for SRT
with exception of Gamma Knife which is dedicated solely for SRS

12. X-ray knife
 The LINAC based technique used multiple non coplanar
arcs of circular beams.
 These beams converges on isocentre placed using
Stereotactic instruments.
 A spherical dose distribution obtained can be
shaped to fit the frame.

13. Fig: X –Ray knife

14. Stereotactic frame
 The Stereotactic frame are attached to patient skull as well as to
couch to provide fixed frame of coordinates
 Several frames have been developed .some notables are Lekshell,
Riechert-Mundinger, Todd wells and Brown –Robert wells.
 Lekshell (Used in AIMS) is engraved with rectilinear coordinates scale
in (mm) . The scale conforms with x y and z direction used in CT and
MR scanning.

15. .
Fig: Lekshell frame

16. Treatment delivery
The patient is made to lie down on the couch and the stereotactic frame is
fixed to the couch.

17.  A localizer is placed on stereotactic frame
 Localizer is removed and treatment will be delivered
.

18.  Geometric accuracy test must be done before SRS/SRT. For that suitable Phantoms
with imageable targets are used.
The phantom consists of test objects Like a cube , sphere, cone and cylinder.
 For SRS/SRT for cones of diameters in range
5- 60mm is used to obtain smaller fields.
Cones
• SRS field are shaped
with MLC microMLC and
gantry rotates to deliver treatment.
MLC MicroMLC

19. CO-60 Based Gamma Knife
 Gamma knife is used to treat tumors, vascular malformations and other
abnormalities in the brain by simultaneous irradiation with large number of iso-
centric gamma ray beams.
 It uses specialized equipment to focus about 200 tiny beams of radiation on a
tumor.
 C0-60 sources are housed in hemispherical orientation and beams are
collimated to focus on single point.
 Hydraulic system is used to control the opening and closing of shielded entrance
door.
 Gamma knife radiosurgery is usually a one time Therapy in a single day.

20. Salient features
• Gamma ray can be delivered by using C0-60 sources housed in cylindrical
configuration
• The beams are collimated using Tungsten collimator of size in mm
• The patient is set up position which is
preselected stereotactic
coordinates.
• Target in brain is localized with stereotactic frame attached to the skull and by
performing imaging studies like CT, MRI

21. • It produce more conformal dose distribution than possible with X-ray knife
• Usually used for treating multiple isocenter ,
more economic and practical compared to x ray knife
because to its simplicity setup.
• Mostly used to treat small lesions

39. Particle beam therapy(photon)
 Proton Therapy is a type of external beam radiation
Therapy.
 Uses proton (Positively charged ) particle to
Treat cancer.
• A machine called cyclotron speedup protons to
High speed which penetrates and travels desired
Depth of body
 Pencil beam scanning is done by sweeping proton
beam laterally over target so that it gives required dose which conforms to the
shape.

40.  Such scanning is achieved through magnetic scanning of thin beamlets of
protons.
 Multiple beam are delivered through different direction.
 Magnet in nozzle steer the proton to conform the target volume as dose is
painted layer by layer.
 Proton has property of Bragg peak that helps to confine the dose within tumor
only reducing dose to nearby tissue
 This provides greater flexibility and control letting proton dose conform more
precisely to the shape of tumor
 Applications: Use in treatment of Eye tumor, Head and neck, Breast cancer,
Lymphoma etc.

42. Dosimetry
 There are three quantities of interest in SRS dosimetry: central axis depth distribution
percentage depth dose or TMR, cross beam profiles and output factors.
Measurement of these quantities is complicated by two factors
 Detector size relative to field dimensions and
 possible lack of lateral charge particle equilibrium.
For central axis depth dose , sensitive volume of detector must be irradiated with
uniform electron fluence because in smaller circular field central axis area of uniform
intensity does not extend beyond few millimetres in diameter . This puts stringent
requirement on detector diameter

43.  For cross beam profile measurement because of steep dose gradient at field
edges , dosimeter must have high spatial resolution to accurately measure
field penumbra.
• Detector size is critical parameter in calculation of output factors in small
field.
• For ultra small field (diameter < 10mm ) films , diodes are most appropriate
detector for profile , depth dose and output factor measurements

44. Quality Assurance
SRS/SRT is a special procedure which requires careful Q.A program to maintain
its original accuracy specification.
There are two categories :
TREATMENT Q.A
AND
ROUTINE Q.A.
Treatment QA involves checking treatment parameters pertaining to patients.
Routine QA is designed to periodically inspect the hardware and software
performance to ensure compliance with original specifications.

45. X- knife QA.
The first procedure in preparing A LINAC for Radiosurgery is to check whether
the lasers are aligned to the point of isocenter.

46.  TEST TOOL
It is used for verification of ODI

47.  ISO-CENTRIC CHECK

48.  MMLC fixed to the gantry

49.  SPOKE TEST – It is done to check Radiation Isocenter.

50.  COLLISION TEST
To check whether the Gantry And the couch will collide during the arc

55. Gamma knife QA

57. Daily QA –LINAC output constancy
Measurement using birdcage

64. AQA radial error should be less than 1mm

65. Daily QA Monthly QA

66. Annual QA

67. SRS/SRT Side effects
 Swelling: Cells lose ability to retain fluid, edema may occur
 Necrosis: Dead tumor cells may cause complications (inflammation,
fibrosis)
 Neurological side effects: Depends on the part of brain receiving
significant radiation - loss of memory, decreased cognitive abilities,
etc. (you are taking out a chunk of brain!)
 Radiation-induced tumor/cancer: Rarely radiation-induced mutations
may result in a new tumor or cancer

68. Conclusion
“Rich only in hope, possessing only incomplete information, incapable
of offering precise techniques, adapted to diverse forms of cancer,
radiotherapy has however obtained definite cures in cases incurable
by surgery.”
Henri Coutard (1876-1950)
Written in 1937
SRS/SRT has great potential but must be executed with care and caution.
It is highly effective: local control rates ≥ 95%.
Low (sub) acute and late toxicity; no adverse impact.
Patient-friendly, non-invasive technique.

69. References
1) The Modern Technology of Radiation Oncology by Jacob Van Dyk ,Medical
Physics Publishing, ISBN:0944838383
2) Physics of Radiation Therapy by Faiz M.Khan, Wolters Kluwer Publications
,5th Edition, ISBN:9781451182453
3) AAPM TaskGroup Reports- TG-142 , TG- 135, TG-178.
4) Annals of surgery by Henri Courtard
5) http://.www.aerb.gov.in
6) http://www.slideshare.net/gammaknife
7) http://www.oncologymedicalphysics.com
8) www.iaea.org/resources
9) www.aapm.org/pubs/reports

70. THANK YOU