Introduction to Cyber-Knife

1. Presenter- Aaditya Sinha
M.Sc Radiotherapy Technology

2. What is a CyberKnife?
A frameless robotic radiosurgery system used for treating benign
as well as malignant tumors and other medical conditions:
• The CyberKnife concept, invented by Dr. John Adler, a
neurosurgeon in Stanford, USA, came into practice by1990s.
• Presently, Accuray Inc., Sunnyvale, CA, USA is the firm
manufacturing the Cyberknife system

3. Stereotactic Radiosurgery/Radiotherapy (SRS/SRT)
• Stereotactic means using a precise 3-D mapping technique to
guide a procedure.
• Radiosurgery refers to stereotactically guided conformal
irradiation of a defined target volume in a single session.
• SRT is delivered in multiple fractions.
• Now-a-days SBRT i.e. Stereotactic Body Radiotherapy is
increasingly being used.

4. Key requirements for optimal SRS/SRT/SBRT
Requirement Rationale
• Small target reducing the volume
improves tolerance
• Sharply defined target no inclusion of normal
tissues
• Accurate dose delivery no margin and hence
smaller volume
• High conformity reduced treatment
volume
• Sharp dose fall-off better sensitive
organs/normal
tissues sparing

5. GTV
CTV
PTV
Target Volumes
• GTV - Gross Target Volume
includes tumor that can be seen in treatment
planning images (typically CT, MR or PET).
• CTV - Clinical Target Volume
includes the GTV plus regional lymph nodes and
tissue adjacent to the GTV that may contain
microscopic tumor cells.
• PTV - Planning Target Volume
includes CTV plus a margin of healthy tissue to
account for inter- and intrafraction organ motion.
In order to treat the CTV, the planner must design a
treatment plan for the PTV.
ICRU50 ICRU62

6. Problem areas in accurate targeting
• Inter-fraction and intra-fraction tumour
movement/shift :
i) Caused by respiratory, skeletal muscular, cardiac
and gastrointestinal systems : intra-fraction
ii) Set-up errors : inter-fraction

7. On-board imaging
• Generally on-board imaging namely portal imaging, CBCT
etc correct for inter-fraction errors such as patient set-up
errors and organ filling errors.

8. Management of Respiratory Motion
• Respiratory gated techniques.
• Breath-hold techniques.
• Forced shallow breathing methods.
• Real-time tumor tracking methods.
• Adding margin around CTV

9. Note of Caution
• Respiratory motion is just one potential source of error
in radiotherapy. Other important errors, particularly for
lung tumors, are gross tumor volume (GTV) and clinical
target volume (CTV) definition variations and set-up
errors.
• Some of these errors are almost an order of magnitude
larger than that of respiration-induced motion. Also, set-
up errors for lung and breast cancer are of the same or a
higher order than that of respiratory motion.

10. • It uses the proprietary tracking technology for motion
management correcting for intra-fraction motion.
• It is the only technology where the beam tracks the tumor
except for MLC based tracking.

11. Various Components of CK
(X-band)

12. Various Components…
• 6 MV Compact X-band linac
• Robot with 6 degrees of freedom
• 12 interchangeable circular collimator
• 5-60 mm dia at SSD 80 cm
• SSD can vary from 65-100 cm
• Orthogonal X-ray system
• Synchrony External tracking system

13. Circular Collimators

14. MLC
With the new InCise Multileaf
Collimator, the CyberKnife M6 Series
is the only clinical solution to
combine the benefits of the Multileaf
Collimator (MLC) beam shaping with
continual image guidance and non-
isocentric, non-coplanar treatment
delivery.

15. 6D Robotic Couch

16. Robotic Couch
• With a full six degrees of freedom, the RoboCouch System can
automatically control anterior/ posterior, superior/ inferior,
left/right, pitch, roll and yaw corrections—for the sub-millimeter
demands of full body radiosurgery and high-precision radiation
therapy.
• It provides access to targets in any part of the body.
• 500 lb. weight capacity.(227 Kg)

17. Synchrony Tracking System
Principles:
The goal of Synchrony is to track the tumor motion in real-time so
that the CyberKnife robot can adjust the radiation beam
continuously throughout the treatment to ensure that the beam
motion follows the motion of the tumor.
Currently, Synchrony is the only system in wide clinical use that can
track tumor motion in 3 dimensions using real-time feedback from
the patient, which does not use continuous fluoroscopy throughout
the treatment.

18. Synchrony Respiratory Tracking System
• Patient wears a vest with optical markers that serve as a surrogate
for tumor position.
• Camera system monitors position of markers.

19. Synchrony Respiratory Tracking System
• Before the treatment, a correspondence model between the
markers and the tumor position is constructed using the camera
and multiple orthogonal X-ray.
• Model is updated continuously during treatment by further x-ray
imaging.
• During delivery, the tumor position is tracked using the live
camera signal and the correspondence model.
• The robotic is moved in real-time to maintain alignment with the
tumor.

20. Plan Prescription
• The prescription isodose for CK is typically 80%
isodose line.
• A plan is considered ideal if 80% of the tumor
volume is covered by the prescription dose. In
some cases, it may be very difficult to achieve this
goal due to the proximity of critical organs and the
larger penumbra of the larger cones.

21. Planning Process
• If tumor tracking is to be done with fiducials, 2-4 gold markers
(0.8 mm dia, 5 mm long) are inserted into or close to the tumor
with CT/USG guidance one week prior to actual planning.
• Breath-hold ( end inspiration/expiration) CT scan is taken for
contouring ,marker identification and DRR generation.
• A 4D CT is done to assess the fiducial motion. If its more than
2mm in any direction, only then Synchrony is used.

22. Tumour Tracking Modeling
• If a fiducial marker is implanted within a tumour or
close to it, their relative motion would be linear
and hence modeling more accurate. Here the
tumour and the markers follow the same
trajectory.
• One marker in the tumour is enough for tracking.
However, at least two need to be implanted to
know of marker slippage.

23. • At the beginning of treatment, a mathematical model
(correspondence between external markers as seen by the
camera and the internal fiducial markers seen by the x-rays)
is built, which is then used to determine the tumor position
in real time.
• Two orthogonal diagnostic images are taken at least 8 times
at different phases of the respiratory cycle.
• By registering these images with 2 DRRs which are
generated from the planning CT, the absolute position of
the tumor relative to the fiducials can be determined.

24. • To build a reliable model, it is best to image once at the
end of inspiration, once at the end of expiration, 3 times at
different phases of inspiration and an additional 3 times at
different phases of expiration—a total of 8 images.
• Each time a pair of orthogonal images is taken
synchronously, they are digitized, positions of internal
fiducial markers are registered, and each image is time-
stamped.

25. CyberKnife Delivery
• Radiation is delivered at a
discrete set of linac positions
called nodes.
• A typical treatment plan will
use 110 nodes distributed
approximately uniformly over
about one half of a sphere
centered on the treatment
site.

26. • The treatment, which generally lasts 30 - 90 minutes,
typically involves the administration of 100 - 200
radiation beams ( from the possible 1200 directions)
delivered from different directions, each lasting from 10
to 15 seconds. The patient may leave the facility
immediately upon completion of the procedure.

27. Applications
• SRS, SRT and SBRT for various sites
• Cranial benign/malignant tumours
• Lung, prostate tumours
• Cranial /extracranial mets

28. Advantage of Cyberknife:
• Frameless
• Fractionated delivery
• Can be used for both intracranial and extracranial
stereotactic delivery.
Disadvantages:
• The use of a pencil beam based delivery is inefficient and
can lead to treatment times that can be several hours.

29. Thank You