IGRT and SBRT Programs with
Siemens Accelerators and ExacTrac
Stereoscopic XX-ray System
Linear Accelerators with features
specifically suitable for SBRT
Dimitris Mihailidis
Mihailidis,, Ph.D.
Charleston Radiation Therapy, Charleston,
Charleston, West Virginia
* Slide courtesy of Brian Kavanagh / University of Colorado
Introduction and Purpose
QUESTION:
Can Stereoscopic x-Ray IG Technology convert a
conventional Siemens (Primus or Oncor) linac into
a “precision” IG - SBRT delivery machine ?
Description of the Systems
Implement Image Guidance (IG) on a
Siemens Linac (Primus or Oncor).
Necessary components to include for IG
upgrade.
Compatibility of components to provide an
IG solution.
Transition to an SBRT program.
Siemens PRIMUS with ExacTrac System
Infrared camera
BrainLab ExacTrac System:
Two X-ray tubes.
Two amorphous silicon detectors (20x20 cm2).
Infrared Polaris system.
Touch screen and arm.
512x512 Matrix
X-Ray phantom.
ISO phantom.
Rando pelvis phantom.
Reference star or markers.
Imaging
panels
In-room monitor
X-ray tube
1
TG-142 requirements for IMRT & SBRT:
Mechanical and radiation isocenter verification:
Siemens linac preparation
Gantry rotation (<1mm diameter)
Collimator rotation (<1mm diameter)
Table rotation (<1mm diameter)
MLC system Quality Assurance:
Leaf position repeatability (±
(±1mm Oncor or ±2mm Primus)
Leaf positional accuracy (1mm at cardinal gantry angles)
Radiation vs. Light coincidence (1mm).
Collimator rotation – radiation isocenter
X-Jaws 0.19 mm
Gantry rotation – radiation isocenter
X-Jaws 1.02 mm
Y-Jaws 0.06 mm
Y-Jaws 0.04 mm
Table rotation – radiation isocenter
X-Jaws 0.44 mm
Y-Jaws 0.41 mm
2
MLC picket fence test for Siemens
Have strong
and
frequent engineering support !
Scan direction
Scan direction
2 cm
center-to-center
The Technology at CRTC for SBRT
• Siemens Primus and Oncor Linacs.
• Philips large bore CT simulator (4D-CT capability).
• Philips Pinnacle3 Treatment Planning System.
• BrainLab ExacTrac 6D-Stereoscopic X-ray Image
Guidance System.
Move on with SBRT
Utilize more accurate patient immobilization
devices.
Utilized 4D-CT simulation for appropriate sites
(e.g., lung, liver, etc), ITV approach.
Utilized highly conformal multi-beam treatment
planning and intensity modulation.
Utilized image guidance for patient daily setup.
Utilized on-line patient surveillance and setup
correction during treatment.
Utilized 5 and 10 mm MLC width for delivery.
Small field size measurements
Planning System Commissioning
Philips Pinnacle3 v8.0m with DMPO in
step--andstep
and-shoot mode.
BEAM MODEL
Model fit to the data
3
Small field size measurements
Detectors for small field measurements
1.00
OUTPUT FACTORS
0.90
0.80
0.1cc Scanning IC
0.70
Diode Perp. (norm to 5x5)
Microchamber
0.60
XV Film
Small fields-MLC shaped
Pinnacle Hi Res
0.50
0.40
0.00
Pinnacle Lo Res
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
4.50
5.00
Direct Machine Parameter Optimization
• DMPO produces final segments at the end of the
optimization process. NO conversion is required.
Automatically converts the ODM to MLC control
points.
• The MLC leaf positions and the weights of the
segments are optimized at once (equivalent to DAO).
• The time to prepare a plan is substantially reduced in
DMPO.
• You can filter the final control points according to
area and monitor units.
How important is the MLC system in
multi--beam SBRT treatment planning?
multi
DMPO
Dosimetric Comparison of MLC systems
Linac
MLC system
MLC width
Siemens Primus (X-jaws) Optifocus double-focused (divergent) - 58 leaves
10 mm
Siemens Oncor (X-jaws)
Double-focused (divergent)- 82 leaves
10 mm
Siemens Artiste (X-jaws)
160MLC (rounded) - 160 leaves
5 mm
Varian Trilogy (tertiary)
Millennium (rounded) - 120 leaves
5 mm
Beam Modulator (rounded) - 80 leaves
4 mm
Elekta MLC (rounded) - 80 leaves
10 mm
HD micro-MLC – 120 leaves
2.5 mm
Elekta Synergy-S BM
Elekta Synergy
Novalis TX (tertiary)
Method of comparison
“RING”: A special ring-structure around the TV, 1 cm expansion of
the TV – to evaluate the sparing of normal structures adjacent to TV.
________________________________________________________________
Paddick, J. Neurosurg. (Suppl. 3) 93:219-222, 2000
CONFORMITY INDEX: CI = ( PIV / PVTV ) / ( PVTV / TV )
CI = 1, perfect conformity
TV = target volume
PIV = prescription isodose volume
PVTV = is the TV included in PIV
Nakamura JL, et al., Int. J. Radiat. Oncol. Biol.
Phys. 51, 1313-1319 (2001).
The IL was chosen according to the criteria:
(1) being the greatest IL that covers 95% of TV while
(2) delivering ≥95% of the prescription dose to 99% of the TV.
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Comparison: Conformity Index
Comparisons: 3D conformal vs. Intensity Modulation
Oncor (10mm)
Artiste (5mm)
Varian (5mm)
NovalisTX (2.5mm)
Synergy (10mm)
SynergyBM (4mm)
Conformity Index (CI)
2.5
Peri-tunoral Ring Volume
4.64 cc Lung target
Oncor (10mm)
Artiste (5mm)
Varian (5mm)
120
NovalisTX (2.5mm)
Synergy (10mm)
2
100
CI
V olum e (% )
1.5
1
0.5
SynergyBM (4mm)
80
60
40
20
0
0
4.64 (Lung-3D)
4.64(Lung-IM)
7.63(Brain-IM)
9.85(Lung-3D)
50%(IM)
25.78(Spine-IM)
80%(IM)
90%(IM)
50%(3D)
80%(3D)
90%(3D)
Isodose line
Target Volume (cc)
3D-CRT vs. Intensity Modulation
Mihailidis, et al., AAPM 2009, Med. Phys. 36, (2009) 2660
Mihailidis, et al., AAPM 2009, Med. Phys. 36, (2009) 2660
Comparison: MLC systems
Comparison: Lung IMRTIMRT- all MLC systems
LUNG: 3D CRT
100% Rx
90% Rx
10mm
80% Rx
10mm
5mm
50% Rx
Oncor: 10 mm
Novalis TX: 2.5 mm
4500 cGy
5mm
2.5mm
4mm
4275 cGy
3600 cGy
Mihailidis, et al., AAPM 2009, Med. Phys. 36, (2009) 2660
Mihailidis, et al., AAPM 2009, Med. Phys. 36, (2009) 2660
Conclusions of comparisons
5mm Varian
2.5mm Novalis TX
SBRT – LUNG
Our study is the first to include the majority of today’s MLC
systems in a comprehensive way and has shown no apparent
indication that smaller MLCs can lead to optimal plans, if
multi-field techniques (IMRT or 3D) are utilized in SBRT.
However, we believe that small tumor volumes would benefit
from small MLC widths and
single fraction SRS, instead.
Tanyi, JA, Radiation Oncology 4:22 (2009)
NO – GATING!
WHY ?
Mihailidis, et al., AAPM 2009, Med. Phys. 36, (2009) 2660
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4D CT Simulation for LUNG SBRT
Patient Immobilization
With arms over the head.
Flat lung board with T-bar holder for the arms.
CT Scanning procedure for moving target
One free breathing scan – 3 mm slices, entire chest.
One shorter, time-correlated scan – 3 mm slices, to
include the tumor area.
Breathing Waveform is acquired along with CT data
using a Bellows or RPM device.
The CT data acquired in one breath can be binned into
10 equally spaced intervals along the waveform and
reconstructed.
The 10 intervals are called Phases.
Vacuum Bag
Maximum Intensity Projection (MIP)
CT data is acquired using a Bellows or RPM
device that records a breathing wave.
Maximum intensity values are assigned to pixels
at locations where a tumor moves to over time.
Are a derived dataset of images that show a
“composite” of the tumor volume over the time
period that the CT data was acquired.
Moving Target virtual simulation - Fusion
MIP dataset
Volume propagation from MIP dataset
to
free breathing dataset
GTV
ITV
Free Breathing
dataset
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Treatment planning
Allow for lowlow-level Intensity Modulation
Multiple non-coplanar beams
Step-and-shoot mode:
• 2-3 segments per beam.
• 50Gy in 5 fxs.
• Optimization objectives
-heart
-ribs
-normal tissues
PTV=ITV + 5mm margin
Mihailidis, et al., AAPM
2009, Med. Phys. 36,
(2009) 2660
www.charlestonradiation.com
DMPO - optimization
DVH results
WE HAVE NOTICED:
2-3 segments allow for
dose compensation due
to lack of resolution of
the 10mm leaf width.
PTV50Gy
ITV
Ipsilateral lung
Mihailidis, et al., AAPM
2009, Med. Phys. 36,
(2009) 2660
www.charlestonradiation.com
ExacTrac setup for lung SBRT
Treatment Isocenter
Virtual isocenter for IG
ET reconstructed views
SBRT - LUNG
Patient setup verification
prior to treatment
IMAGE GUIDANCE
7
Fusion preparation
Before Fusion - misalignment
ET x-ray
Excluded from fusion area
DRR
After fusion – shifts to be implemented
Match of x-ray and DRR
SBRT - Brain
SHIFTS
Patient setup and immobilization
Fusion MRI – TP CT
ExacTrac IR markers
TP CT
www.charlestonradiation.com
MRI
Vargo J, Plants B, Welch C, Mihailidis D, et al., ASTRO 2010, IJROBP 78 (No. 3 Suppl), S279 (2010)
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Sample isodose and DVH
SBRT brain positioning and planning
Prescription:
40 Gy in 5 fxs
788 MU
objectives
Multiple non-coplanar beams
Vargo J, Plants B, Welch C, Mihailidis D, et al., ASTRO 2010, IJROBP 78 (No. 3 Suppl), S279 (2010)
PTV
Vargo J, Plants B, Welch C, Mihailidis D, et al., ASTRO 2010, IJROBP 78 (No. 3 Suppl), S279 (2010)
Patient setup with IR markers
SBRT - BRAIN
Patient setup verification
prior to treatment
IR marker
IMAGE GUIDANCE
from TPS
www.charlestonradiation.com
Fusion
Continuous IG
BEFORE
DRR
Allow for live patient survaillance with the IR
camera and markers.
Perform a second IG verification between
treatment fields (residual shifts).
Compare reference orthogonal treatment ports
with orthogonal DRRs.
Keep rotations to less than 3° if possible,
otherwise…improvise.
SHIFTS
DRR
x-ray
x-ray
Wood Shims
AFTER
www.charlestonradiation.com
www.charlestonradiation.com
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6D-corrections and residual setup errors
6D-IGRT accuracy: Infrared vs. stereoscopic x-ray
Comply with published recommendations:
Conclusions
ExacTrac Stereoscopic x-Ray IG system, in
combination with other technologies, provides
accurate IG that allows the implementation of an
SBRT program,
IF
additional precautions are taken.
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THANK YOU !
NRAO Green Bank Observatory, West Virginia
http://www.gb.nrao.edu/
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