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IGRT Robotica
G.Beltramo
Centro Diagnostico Italiano
Varese 13 Giugno 2009
Image-Guided Radiation Therapy
“Any use of imaging within the radiation
treatment room, to improve the precision
of radiation-therapy delivery”
“Use of any planar imaging, volumetric
imaging, or volumetric ciné imaging, marker
localization, marker tracking, patient surface
imaging, patient surface tracking to improve the
precision of radiation therapy delivery.”
“IGRT
is the process of in-room
imaging that guides the
radiation delivery.”
Focus: Image guided RT Intervention
Three essential steps:
Acquire an image
• Acquire the positional information of the target, target surrogates, or avoidance
structures
Obtain “target” registration error
• Image registration
• Deviations from the original plan
Perform an intervention
• Correction strategies
– Inter fraction/intra fraction, online/offline etc.
Advances in radiation technology
Stereotactic Radiosurgery System
CyberKnife®
In 1991 Jonh Adler, an american neurosurgeon, develop a delivering
stereotactic radiosurgery system without the need for rigid immobilization
CyberKnife® Robotic Radiosurgery
• Non-coplanar treatment
delivery
• Total of more than 1500
different beams
• Delivery of 150 to
200 uniquely angled
beams
per fraction
Image courtesy of Georgetown University Hospital
Need X ray vision!
• The target volume is located on X rays (orthogonal or
stereoscopic) with fiducial markers or without them (if the
target volume can be seen on X rays)
• The images are to be fused and registered with the
pretreatment DRR’s
• The required shifts are calculated using customized
software.
• Shifts are made
Stereotactic Radiosurgery
System CyberKnife®
Cyberknife (CK) therapy. CK (Accuray, Inc.,
Sunnyvale, California) is an image guided,
frameless, radiotherapy device with a
compact linear accelerator installed on an
industrial-derived robotic arm, The
intelligent arm has the capability of rotating
around 6 axes with millimetric accuracy
allowing a stereotactic radiosurgery (SRS)
with high radiation doses to relatively small
lesions. The treatment unit can verify target
position with a real-time tracking during
radiation delivery using two kV X-ray sources
mounted on the ceiling and two amorphoussilicon image detectors mounted on the floor
on either side of the patient in an orthogonal
geometry to detect bony landmarks or
fiducial markers within or near the target.
The targeting system continuously acquires
radiographs that are compared with the
digitally reconstructed radiographs (DRR)
derived from the treatment planning CT
scans to update the changes in target
position which are compensated by
adjusting the aim of the robotic arm [ ].
Dx X-Ray Sources
Amorphous Silicon
Detectors
Cyberknife data acquisition
Image guidance
Stereographic X-ray images are
compared with DRRs or fiducial
positions
Robot corrects after each
stereographic X-ray image
acquisition
Robot can correct:
± 10 mm all components
± 1º roll
± 1º pitch
± 3º yaw
Flowchart of the patient set up and delivery process in Cyberknife treatment
Planar X Rays (2D+)
Advantages
–
–
–
–
–
Fast image acquisition (single or fluoroscopic modes)
High temporal resolution
X-ray
Tracking
source
B
Beam by beam correction
Motion management
Disadvantages
Image A
– Use of target surrogates (in most situations)
– Obstructions in image viewing angles (anatomies or couch
support in the beam path)
– Not easy to reconstruct 3D dose distributions
“On-line Correction”
X-ray
source
A
Y
Cam
era
A
Pit
ch
Cam
era
B Image
B
Analysis of images and/or related data for potential corrections of the delivery of
the current fraction (i.e. analysis performed while the patient is still on the
treatment couch).
Verification of treatment accuracy
Skull may be good surrogate for brain
Verification of treatment accuracy
• Bone or marker???
spine bone poor surrogate for extracranial cancer
Verification of treatment accuracy
Accuracy of radiotherapy delivery depends on the visualisation of implanted gold fiducials at
the time of treatment and comparison with references images obteined during treatment
planning, . The advantage of Cyberknife tracking sistem is to verify in every step of
treatment the real position of neoplstic target and the possibility to adjust the aim of robotic
arm if the target position change during radiotherapy treatment
Accuracy of fiducial targetting
Total error in patient pose is dependent on the
number of fiducials being tracked
> 6 fiducials adds little more improvement
Error in translations unaffected by spacing
Error in rotation is  50% by doubling the
distance between fiducials
mean targeting error
3 fiducials significant improvement in targeting
accuracy
0.5
0.4
0.3
0.2
0.1
0
2
3
4
5
number of fiducials
6
Rigid body constraint
Distances between like fiducials compared
Histogram of prostate
volume as a function of
time duration and shift
Accuracy of fiducial targetting
Percentage of data set of
having a movement as a
function of time
Rigid body error curve of three fiducials
for four rappresentative patients
Inter-fractional motion of the prostate
during hypofractionated radiotherapy
CDI Cyberknife experience
Real Time Imaging
Imaging with a temporal resolution that’s
sufficient to capture the trajectory of a moving
or changing subject. Real time IGRT correction
refers to frequent imaging while the treatment is
being delivered, with repositioning based on
that imaging.
real-time monitoring of any parameter must be fast
enough to modify the treatment in order to account
for the impact of that parameter on treatment.
State of the art in room techniques for
respiratory motion management
Technologies available
•
•
•
•
•
•
•
•
Optical
MV/EPI
kV X ray
kV/MV/Optical
4D CBCT/CT
Electromagnetic
Ultrasound
MRI
Respiratory Guided Radiation
Therapy
Infrared LED-camera system records the respiration
cycle
Real time
moving the treatment beam as the target moves
Motion management methods
CyberKnife® Robotic Radiosurgery
• Accuracy
– Total targeting accuracy
• Targets not affected by
respiration: 0.5 millimeter**
• Targets that move with
respiration: 0.7 millimeter***
– Targeting accuracy sustained
throughout the treatment
* Kuka KR240-2 Specification 04.2004.05
** Muacevic, A., Staehler, M., Drexler, C., Wowra, B., Reiser, M. and Tonn, J. Technical description, phantom accuracy and clinical feasibility for fiducial-free
frameless real-time image-guided spinal radiosurgery. J Neurosurgery Spine. Xsight accuracy specification of .95 mm.
***
Dieterich S, Taylor D, Chuang C, Wong K, Tang J, Kilby W, Main W. The CyberKnife Synchrony Respiratory Tracking System: Evaluation of
Systematic Targeting Uncertainty. Synchrony clinical accuracy specification of 1.5 mm for moving targets
Patient fixation - Stereotactic Elekta® Body Frame
• Individually fitted vacuum pillow
• Laser system for tattoos
• Device for diaphragm compression
(breathing tumor movements >10 mm at fluoroscopy)
Methods to avoid geographic miss
- ITV (abd compression), breath hold (ABC),
gating, and tracking
Cyberknife Radiosurgery : clinical
rationale
Take Home Messages
(Target Delineation)
•
With robotic IGRT, treatment precision may be improved:
More accurate contours are REQUIRED
• Inaccurate contours could introduce unexpected target
miss or increased toxicities
Use For Tracking
 Cannot be extracted
 Migration
 Obscured
Day 0: fiducial insertion
Day 7: treatment planning
TC. fiducial migration
Day 10: missing
Inaccurate target delineation
IMAGE FUSION TC-RM
Use CT for geometric accuracy
Use RM for target delineation
Clinical use of this tecnique for treatment planning
has resulted in improvements in localization of
treatment volumes and critical structures in the brain
Kessler M.L.1991
Lattanzi J.P.1997
Image guidance facilitates targetting
TC-MRI image Fusion
MRI for Target Delineation
Advantages
•
•
•
•
•
•
Superior soft tissue image quality
For some tumors - greater sensitivity
Greater accuracy - delineation of some normal tissues
Functional information – normal tissues
Biological information – TME, blood flow, hypoxia
No radiation dose
Disadvantages
•
•
•
•
•
•
Lack of specificity for tumor vs. other pathological states
Multiple effects that can lead to image distortion
Does not provide relative radiation attenuation
Requires fusion of grayscale images with CT dataset
Motion artifact
Cost
3D CRT and IMRT aim to achieve better locoregional control
and improve survival by radiation dose escalation, but such
techniques demand more accurate localization of tumor and
surrounding normal tissues
Imaging in Target Delineation
PET in Target Definition
Use of PET imaging to reduce
interobserver
variations in contouring
STEENBAKKERS et al., IJROBP, Vol64, pp435, 2006
Do SUVs mean anything?
Uncertainties in Manual Volume
Alignment
Differences in Image Interpretation
• Inter-observer variation
Contours may not be drawn perfectly
One person’s alignment may not agree with another person’s judgment
• Impact of organ deformation
Imperfect alignment
SBRT theoretical basis
Operable lung cancer patients
Extent of resection impacts local control
(e.g., wedge vs. lobectomy – LCSG trial)
Local control impacts survival
Goal with SBRT in inoperable patients
should be very high local control until
proven otherwise
At treatment
After 3 months
After 12 months
SBRT for early stage lung carcinoma
Large Japanese Study (Onishi, 2007)
Indiana phase I trial
SBRT toxicity
Respect Normal Tissue Constraints
Respect Normal Tissue Constraints
Organ at risk dose coinstrain
Respect Normal Tissue Constraints
GRADE II
GRADE III
GRADE IV
3 months post SBRT
6 months post SBRT
12 months post SBRT
Local Therapy and Image-Guidance
• Radiation therapy is a proven local therapy.
• Increased precision in therapy offers:
– Reduce severity and risk of therapy-induced complications.
– Increase both quality and probability of success.
• Further potential:
– Broaden application of proven therapies.
– Permit new therapies that are intolerant to geometric
imprecision.
• Addressing geometric uncertainties may expose other
factors determining outcome.
Not a single IGRT solution can correct
all sources of uncertainties
Systematic
Random
Inter-fractional
Intra-fraction
Shape Variations
Time Trends
The living patient and the
dynamic treatment problem
What could possibly go wrong and how could that happen?
Inadequate implementation of IGRT technology for the treatment site
What effects would such a failure produce?


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Suboptimal treatment
Failure to control cancer
Increased toxicities
Waste of resources
Clinical benefit of image guided
robotic radiotherapy
Stereotactic body radiotherapy (SBRT) is the Latest
Generation of “Targeted “ therapies for radiation