3D Surface Imaging
for PBI Patient Setup
G.T.Y. Chen1, Ph.D., M. Riboldi2, Ph.D.
Christoph Bert3, Ph.D., D.P. Gierga1, Ph.D.
1Massachusetts
General Hospital
Harvard Medical School
2TBMLab - Department of Bioengineering
Politecnico di Milano University
3GSI
Darmstadt, Germany
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„WG Conner 1975 – Motion detection
/cancellation imaging
JA Purdy 1978
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Video-based patient set-up
2-Dimensional:
3-Dimensional:
• laser interferometry
• video images with single /
orthogonal cameras
- surface height maps
• stereo-photogrammetry
- point-based registration
- surface registration
accuracy
simplicity
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Marco Riboldi
3-D point-based stereo-photogrammetry
Control room
Bunker
Sync-power and composite video
gantry
Motion
Analyzer
Digital data
TVC 2
radiation
beam
IR flash
CPU
3-D markers coordinates
Isocenter localization
control points
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TVC 1
IR flash
Applications of 3-D point-based stereo-photogrammetry
G Baroni, CAS 2000
Breast irradiation
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3-D surface scanning
G Baroni, MBEC 2003
Breast irradiation
Opto-electronic surface sensing
Hybrid registration (surface fiducials / laser spots
JW Sohn, AAPM 2004
Breast irradiation
Handheld laser scanning
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Recent References / Others
2-D patient set-up:
1.
2.
Milliken BD, Rubin SJ, Hamilton RJ, Johnson LS, Chen GT. Performance of a video-image-subtraction-based patient
positioning system. Int J Radiat Oncol Biol Phys. 1997 Jul 1;38(4):855-66.
Johnson LS, Milliken BD, Hadley SW, Pelizzari CA, Haraf DJ, Chen GT. Initial clinical experience with a video-based
patient positioning system. Int J Radiat Oncol Biol Phys. 1999 Aug 1;45(1):205-13.
3-D point-based stereo-photogrammetry:
1.
2.
3.
4.
Rogus RD, Stern RL, Kubo HD. Accuracy of a photogrammetry-based patient positioning and monitoring system for
radiation therapy. Med Phys. 1999 May;26(5):721-8.
Baroni G, Ferrigno G, Orecchia R, Pedotti A. Real-time opto-electronic verification of patient position in breast cancer
radiotherapy. Comput Aided Surg. 2000;5(4):296-306.
Soete G, Van de Steene J, Verellen D, Vinh-Hung V, Van den Berge D, Michielsen D, Keuppens F, De Roover P,
Storme G. Initial clinical experience with infrared-reflecting skin markers in the positioning of patients treated by
conformal radiotherapy for prostate cancer. Int J Radiat Oncol Biol Phys. 2002 Mar 1;52(3):694-8.
Weiss E, Vorwerk H, Richter S, Hess CF. Interfractional and intrafractional accuracy during radiotherapy of
gynecologic carcinomas: a comprehensive evaluation using the ExacTrac system. Int J Radiat Oncol Biol Phys. 2003
May 1;56(1):69-79.
Surface registration:
1.
2.
3.
4.
Moore C, Lilley F, Sauret V, Lalor M, Burton D. Opto-electronic sensing of body surface topology changes during
radiotherapy for rectal cancer. Int J Radiat Oncol Biol Phys. 2003 May 1;56(1):248-58.
MacKay RI, Graham PA, Logue JP, Moore CJ. Patient positioning using detailed three-dimensional surface data for
patients undergoing conformal radiation therapy for carcinoma of the prostate: a feasibility study. Int J Radiat Oncol
Biol Phys. 2001 Jan 1;49(1):225-30.
Baroni G, Troia A, Riboldi M, Orecchia R, Ferrigno G, Pedotti A. Evaluation of methods for opto-electronic body
surface sensing applied to patient position control in breast radiation therapy. Med Biol Eng Comput. 2003
Nov;41(6):679-88.
Sohn J, Kim S, Chvetsov A, Suh T, Jin H, Farr J. Three-Dimensional Surface Image Registration For Image-Guided
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IMRT To Breast. AAPM 2004 Proceedings.
Clinical Implementation of
IGRT for PBI : Microcosm
„ Multiple Approaches to IGRT
„ Organ deformation
„ Respiration
„ Quantify accuracy of methods
„ Apply
statistical rigor to IGRT
„ Etc…
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Challenge: Setup of Breast
•Irradiate involved quadrant of breast (vs. whole)
•4.0 Gy X 8 fractions BID / 4 days (vs. 6 wks)
•Escalate dose; minimize NT irradiation
Mini tangents and electron boost
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Imaging Options
„
Image target (seroma) directly (in room CT)
„
Surrogates (more commonly used)
Skin tattoos – aligned to lasers
„ Chest wall – imaged in radiographs
„ Breast surface – 3D video imaging (new)
„ Clips near seroma – imaged by radiographs
„
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Sources of Uncertainty
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Elasticity of skin, arm position / lasers
Chest wall is weakly coupled to tumor / breast
tissue
Skin /seroma correlation - deformation affects
accuracy
Clip migration / seroma shrinkage affects
radiographic accuracy
Conebeam CT –before not during Rx
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Outline:
1)
2)
3)
4)
5)
System Description
System Performance
Patient Studies
Target Registration Analysis
Summary
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1. Surface Imaging Hardware
Linac1
Linac2
(Protons)
POD 1
POD 2
AlignRT
Gantry
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Each pod contains….
Speckle
Camera
Flash
Projection
Texture
Cam
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Speckle
Camera
Speckle image
„
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Two camera pods
Flash mode
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„
„
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Speckle pattern
6 images captured
Surface coords in 3D
Surface matching to
maximize
congruence between
reference and Rx
surfaces
Torso phantom
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Reconstructed surface image
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Wire Frame Obj images
Zoomed Surface Patch
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Interactive Demo
„
„
Use file Marco 2006 phantom.obj
D:\Research Projects 06\spine 3d
video\viewer\SurfaceView.exe
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3D Surface Alignment Process
(analogous to conventional IGRT)
reference surface (CT or 1st Rx)
„ Acquire daily surface image (after laser
setup)
„ Match daily 3D image with ref image
through surface matching
„ Adjust patient position
„ (Verify post move)
„ Define
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Alignment Screen
ROI
4 DOF
Standard Couch
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6 DOF
2.Characterize System Performance
What is the smallest misalignment detectable by
this 3D video system?
Performed phantom and calculational experiments
to measure system performance.
C. Bert et al Medical Physics 2005, M Riboldi 2006
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Ground Truth
High precision mechanical stage
(digital micrometer, 1/100 mm)
Breast phantom
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Phantom Surface Model
ROI
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Determine System Accuracy
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Acquire reference surface
Move mechanical stage known amount
Acquire “daily” surface image / query system –
how much did it move?
Compare ground truth (known move) with
AlignRT calculated shift.
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Phantom Study Results
•18 readings / data points
•range of shifts: [-2, +2] mm in each direction (VRT, LNG, LAT)
•compared AlignRT-suggested shifts vs. digital micrometers (ground truth)
Translation differences [mm]
VRT LNG LAT 3-D
MEAN
0.011 0.011 0.011
0.1
1SD
0.144 0.144 0.144 0.227
„Minimum detectable translational shifts is sub-mm.
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Phantom virtual experiment
High precision mechanical stage (digital micrometer, 1/100 mm)
Can system detect small angular misalignments?
VRT
LNG
LAT
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Results – 6 DOF transformation parameters
Virtual phantom experiment
0.5
mean±SD
differences [mm] [deg]
0.4
0.3
0.2
0.1
0
-0.1
-0.2
-0.3
-0.4
-0.5
VRT
LNG
LAT
ROT
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PR1
PR2
3.Patient Studies
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Analyze multiple methods of PBI setup (Laser,
Chest Wall, Iris, AlignRT) Comparative /
quantitative analysis of method accuracy.
Metric: residual displacements on target localization
after alignment (Target Registration Error)
Data analysis performed on a statistical basis (non
parametric Friedman ANOVA and Wilcoxon tests)
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Patient Imaging Protocol
Orthogonal
IRIS images:
Clip based move
Patient aligned
by lasers
Image
SMT
Image
SML
DRRs
from
CT
Treat
Image
SME
SMT1 as reference for
VisionRT TRE
evaluation
SMR
from
CT
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Breast Alignment Analysis
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4.Target Registration Error
„
„
The TRE is the vector difference between the
target as aligned by method a,b,c… and ground
truth.
Ground truth: defined by clips (DRRs, Planning
CT)
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Laser TRE
„
Align breast by laser; take radiographs of clips (ground
truth). Calculate shifts needed to bring clip into congruence
with ref image clip position (TRE of Lasers)
Lasers
GT
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Chest Wall (CW) TRE
„Begin with perfect IRIS clip alignment; align CW to ref DRR;
vector difference is CW TRE
Ant
Inf
Clips
Ant
Sup
TT
Inf
Clips
Sup
T
T
Chest Wall
Chest Wall
Post
Post
Chest Wall alignment
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AlignRT TRE
Begin with perfect IRIS clip alignment; match surfaces; apply
transformation to isocenter. Difference vector is AlignRT
TRE.
Surface
mismatch
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Matched
surfaces
TRE
IRIS (radiographic) System
Berbeco et al Phys Med Biol 2004:49:243-257
X-ray Tube retract
IRIS
Steve Jiang
Greg Sharp
Ross Berbeco
Detector Arms retract
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Radiographic (IRIS) TRE
„
Acquire IRIS radiographs; calculate shifts; make shifts; re-image,
DIPS. IRIS TRE is inexactness in repositioning patient EXACTLY to
calculated shift; ie residual error in setup.
IRIS alignment
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TRE Analysis Results
TRE analysis
1.4
1.2
Medians
Laser: .79 cm
Iris: .22
VRT .32
CW: .57
3D TRE [cm]
1.0
0.8
0.6
0.4
0.2
0.0
Median
25%-75%
Min-Max
-0.2
Laser
VisionRT
Iris
CW
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Statistical Analysis
• Is there a meaningful difference between Laser, Iris, Chest Wall
and VisionRT TREs?
YES -> Friedman ANOVA test (p<0.00004)
• Where is the difference?
Wilcoxon rank test:
LASER vs IRIS
p<0.0037
LASER vs AlignRT
p<0.0044
IRIS vs AlignRT
p<0.21
CW vs LASER
p<0.11
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Statistical Analysis Results
• Laser, Iris, CW and VisionRT can be divided in 2 groups, in terms
of TRE results:
CW
Iris
Laser
AlignRT
Median TRE
Median TRE
≈ 6-8 mm
≈ 2-3 mm
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Question
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If the intrinsic accuracy of surface based
alignment is <0.5mm (as shown in precision
phantom experiments), then why are patient
TRE’s on the order of 3mm?
(TRE of IRIS radiographic clip alignment is
about 2mm)
Deformation? Respiration? Other effects?
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SMT2
SMT3
SMT4
SMT5
SMT6
SMT7
Is there breast deformation?
Patient 4: Generally, reference surface and
treatment surfaces are within 2mm after
6 DOF fit. (green areas)
SMT8
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Patient 5
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Can we use CT Breast Surfaces
as reference image?
Rx: Rt Breast
Rx: Lt Breast
Estimated magnitude –using GE Workstation to measure –
Pt 4 ~ 5 mm; Pt 5 ~ 3-4 mm
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Texture Images reveal setup
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Ongoing Studies:
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TRE as a function of breast size and height
above chest wall.
Protocol extended to 300 PBI patients.
Intra-fractional dosimetric variations due to
breathing
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Why surface imaging if we have
ground truth by clips?
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Faster –guide to optimal position, verify as
needed
Reduce radiation in comparison to radiographs
Surveillance during Rx
Not every machine has conebeam CT or OBI
Applications in charged particle beam
radiotherapy.
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5.Summary
ƒ Determined that TRE of 3D surface imaging
system superior to conventional methods.
ƒ Applied statistics to provide significance
ƒ Respiration remains issue if accuracy < 2
mm is desired.
ƒ Deformation is minimal in patients studied
ƒ 3D technology promising for PBI setup
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Acknowledgements
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Steve Jiang ,Greg Sharp, Julie Turcotte
Simon Powell, Alphonse Taghian, Angela Katz,
Ellen Kornmehl
MGH Radiation Therapists
Technical advice: Norman Smith / Ivan Meir
VisionRT
Study conducted under IRB protocol.
AAPM 2006
References
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Bert, C et al: A phantom evaluation of a stereovision surface imaging system for radiotherapy
patient setup Med Phys 32:9 2005
Bert, C. et al: Initial Clinical Experience with
Surface Imaging for PBI: Int J Rad Onc Bio
Phys March 15, 2006
Riboldi, M: submitted for publication 2006
Gierga, DP: Oral presentation at ASTRO 2006
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