SBRT&StereoscopicIGRT_2012 [Compatibility Mode]

IGRT and SBRT Programs with
Siemens Accelerators and ExacTrac
ExacTrac
Stereoscopic XX-ray
XX-ray
ray System
System
Dimitris Mihailidis Mihailidis, , Ph.D.
Charleston Radiation Therapy, Charleston, West Virginia
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
BrainLab ExacTrac System:
Two X-ray tubes.
Two amorphous silicon detectors (20x20 cm 2 ).
Infrared Polaris system.
Touch screen and arm.
512x512 Matrix
X-Ray phantom.
ISO phantom.
Rando pelvis phantom.
Reference star or markers.
Linear Accelerators with features
specifically suitable for SBRT
* Slide courtesy of Brian Kavanagh / University of Colorado
Introduction and Purpose
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
In-room monitor
Infrared camera
Imaging
panels
X-ray tube
1

Siemens linac preparation
Gantry rotation – radiation isocenter
X-Jaws 1.02 mm
Y-Jaws 0.06 mm
TG-142 requirements for IMRT & SBRT:
Mechanical and radiation isocenter verification:
Gantry rotation (

Scan direction
MLC picket fence test for Siemens
center-to-center
2 cm
The Technology at CRTC for SBRT
• Siemens Primus and Oncor Linacs.
Scan direction
• Philips large bore CT simulator (4D-CT capability).
• Philips Pinnacle 3 Treatment Planning System.
• BrainLab ExacTrac 6D-Stereoscopic X-ray Image
Guidance System.
Planning System Commissioning
Philips Pinnacle Pinnacle3 v8.0m with with DMPO in in
step step-and and-shoot shoot mode.
Have strong
and
frequent engineering support !
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
Model fit to the data
BEAM MODEL
3

DMPO
1.00
0.90
0.80
0.70
0.60
0.50
Small field size measurements
OUTPUT FACTORS
0.1cc Scanning IC
Diode Perp. (norm to 5x5)
Microchamber
XV Film
Small fields-MLC shaped
Pinnacle Hi Res
Pinnacle Lo Res
0.40
0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00
Direct irect Machine achine Parameter arameter Optimization ptimization
• 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.
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
Elekta Synergy-S BM Beam Modulator (rounded) - 80 leaves 4 mm
Elekta Synergy Elekta MLC (rounded) - 80 leaves 10 mm
Novalis TX (tertiary) HD micro-MLC – 120 leaves 2.5 mm
Detectors for small field measurements
How important is the MLC system in
multi multi-beam beam SBRT treatment planning?
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.
________________________________________________________________
CONFORMITY INDEX:
TV = target volume
PIV = prescription isodose volume
PVTV = is the TV included in PIV
Paddick, J. Neurosurg. (Suppl. 3) 93:219-222, 2000
CI = ( PIV / PVTV ) / ( PVTV / TV )
CI = 1, perfect conformity
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.
4

CI
Comparison: Conformity Index
2.5
2
1.5
1
0.5
0
Conformity Index (CI)
4.64 (Lung-3D) 4.64(Lung-IM) 7.63(Brain-IM) 9.85(Lung-3D) 25.78(Spine-IM)
Target Volume (cc)
3D-CRT vs. Intensity Modulation
Mihailidis, et al., AAPM 2009, Med. Phys. 36, (2009) 2660
Oncor (10mm)
Artiste (5mm)
Varian (5mm)
NovalisTX (2.5mm)
Synergy (10mm)
SynergyBM (4mm)
Comparison: MLC systems
Mihailidis, et al., AAPM 2009, Med. Phys. 36, (2009) 2660
LUNG: 3D CRT
Oncor: 10 mm Novalis TX: 2.5 mm
4500 cGy
3600 cGy
Conclusions of comparisons
4275 cGy
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)
5mm Varian
2.5mm Novalis TX
Mihailidis, et al., AAPM 2009, Med. Phys. 36, (2009) 2660
Comparisons: 3D conformal vs. Intensity Modulation
V olum e (% )
120
100
80
60
40
20
0
Peri-tunoral Ring Volume
4.64 cc Lung target
50%(IM) 80%(IM) 90%(IM) 50%(3D) 80%(3D) 90%(3D)
Isodose line
Oncor (10mm)
Artiste (5mm)
Varian (5mm)
NovalisTX (2.5mm)
Synergy (10mm)
SynergyBM (4mm)
Mihailidis, et al., AAPM 2009, Med. Phys. 36, (2009) 2660
Comparison: Lung IMRT- IMRT all MLC systems
10mm
5mm 2.5mm
10mm 5mm
4mm
Mihailidis, et al., AAPM 2009, Med. Phys. 36, (2009) 2660
SBRT – LUNG
NO – GATING!
WHY ?
100% Rx
90% Rx
80% Rx
50% Rx
5

Patient Immobilization
With arms over the head.
Flat lung board with T-bar holder for the arms.
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.
4D CT Simulation for LUNG SBRT
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.
Moving Target virtual simulation - Fusion
GTV
MIP dataset
Volume propagation from MIP dataset
to
free breathing dataset
ITV
Free Breathing
dataset
6

Treatment planning
DMPO - optimization
SBRT - LUNG
Patient setup verification
prior to treatment
IMAGE GUIDANCE
Multiple non-coplanar beams
PTV=ITV + 5mm margin
www.charlestonradiation.com
WE HAVE NOTICED:
2-3 segments allow for
dose compensation due
to lack of resolution of
the 10mm leaf width.
Mihailidis, et al., AAPM
2009, Med. Phys. 36,
(2009) 2660
Allow for low low-level level Intensity Modulation
Treatment Isocenter
DVH results
Step-and-shoot mode:
• 2-3 segments per beam.
• 50Gy in 5 fxs.
• Optimization objectives
-heart
-ribs
-normal tissues
Mihailidis, et al., AAPM
2009, Med. Phys. 36,
(2009) 2660
Ipsilateral lung
ExacTrac setup for lung SBRT
Virtual isocenter for IG
ITV
PTV 50Gy
www.charlestonradiation.com
ET reconstructed views
7

ET x-ray
DRR
Before Fusion - misalignment
After fusion – shifts to be implemented
Match of x-ray and DRR
SHIFTS
Patient setup and immobilization
ExacTrac IR markers
www.charlestonradiation.com
Excluded from fusion area
Fusion preparation
SBRT - Brain
Fusion MRI – TP CT
TP CT MRI
Vargo J, Plants B, Welch C, Mihailidis D, et al., ASTRO 2010, IJROBP 78 (No. 3 Suppl), S279 (2010)
8

SBRT brain positioning and planning
Multiple non-coplanar beams
Vargo J, Plants B, Welch C, Mihailidis D, et al., ASTRO 2010, IJROBP 78 (No. 3 Suppl), S279 (2010)
DRR
x-ray
DRR
SBRT - BRAIN
Patient setup verification
prior to treatment
IMAGE GUIDANCE
Fusion
x-ray AFTER
SHIFTS
BEFORE
www.charlestonradiation.com
Prescription:
40 Gy in 5 fxs
788 MU
Sample isodose and DVH
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
from TPS
IR marker
Continuous IG
objectives
www.charlestonradiation.com
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.
Wood Shims
www.charlestonradiation.com
9

6D-IGRT accuracy: Infrared vs. stereoscopic x-ray
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.
6D-corrections and residual setup errors
Comply with published recommendations:
10

THANK YOU !
NRAO Green Bank Observatory, West Virginia
http://www.gb.nrao.edu/
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