Image Acquisition and Processing
for Adaptive Radiotherapy
Part II
Jan-Jakob Sonke
Disclosure
• Our department has research collaborations
with:
• Elekta Oncology Systems
• Philips Radiation Oncology Systems
• Ray Search Laboratories
• Our department licenses software to:
• Elekta Oncology Systems
Acknowledgements
Tom Depuydt, Mischa Hoogeman,
Matthias Guckenberger, Simon van
Kranen, Marcel van Herk, David Jaffray,
Marc Kessler, Maddalena rossi
1
Introduction
Many In-room Imaging Systems
Multimodality Images
2
Jaffray / PMH
‘Adaptive’
Adaptive Radiotherapy
Real time
On-line
Off-line
Temporal Scales of Intervention
Setup Errors
The patient moves from day to day
Organ Motion
Organs move
from day to day
3
How can we solve this problem ?
1. Use large margins, irradiating
too much healthy tissues
2. Use small margins, and risk
missing the target
3. Or: use image guided radiotherapy
Safety Margins
Verellen et al. Nature Reviews Cancer 2007
Pop-Quiz #1
What is the purpose of IGRT?
19%
19%
20%
20%
22%
1.
2.
3.
4.
5.
Make pretty images
Minimize setup error
Quantify organ motion
Reduce PTV margins
Sell more expensive treatment machines
4
Pop-Quiz #1
What is the purpose of IGRT?
1.
2.
3.
4.
5.
Make pretty images
Minimize setup error
Quantify organ motion
Reduce PTV margins
Sell more expensive treatment machines
4) Seminars in Radiation
Oncology Volume 17, Issue 4
Quantification of
Organ Motion
Repeat Contouring
5
Repeat Contouring
LR
(cm)
CC
(cm)
AP
(cm)
Mean
0.10
0.31
1.14
SD
0.13
0.31
0.94
Image Registration
Image Registration
Finding geometrical correspondences
between imaging data sets (2D/3D/4D) that
differ in time, space, modality and/or subject
6
What is an Image
An image is a N-dimensional mathematical function
mapping coordinates to intensity values
Principle of Image Registration
Fixed Image
Interpolator
Transformer
Floating Image
Degrees of Freedom
PET/CT
MR - CT
Marc Kessler / UM
4D CT
0?
3 to 6
3xN
None ?
Few
Many
7
Transformations
Non Affine
(local) Rigid registration in 3D:
• 3 Translations
• 3 Rotations
6 Degrees of Freedom (DOF)
e.g. Couch corrections
Translations
Rotations
Scaling
Shearing
General Framework for Image Registration
Fixed
image
Similarity
Metric
Optimizer
Mapped
Image
Floating
image
Adjusted
Parameters
Interpolator
Transformer
Geometric
Transformation
Possible images or scans
“Fixed”
“Floating”
Application
DRR – radiograph registration for
MV or kV setup verification
CT – CBCT registration for image
guided radiotherapy
MRI – CT registration for MRI
guidance
Floating image is manipulated during image registration operation (arbitrary choice)
8
General Framework for Image Registration
Fixed
image
Similarity
Metric
Mapped
Image
Floating
image
Optimizer
Adjusted
Parameters
Interpolator
Transformer
Geometric
Transformation
Chamfer Matching
•
A two step procedure
1. Segment features in both scans
2. Minimize the distance between the features
Chamfer matching
segmentation
Segment all voxels above a
certain intensity
9
Chamfer matching
distance transform
Calculate for every voxel
the distance to the nearest
feature
Chamfer matching
minimize (mean absolute) distance
Very fast (1 s): well suited
for bony anatomy alignment
Minimize the sum of all distances
for the floating images in the
corresponding distance transform
Grey Value / Intensity matching
Uses all pixel values in ROI: e.g., sum of squared differences
Somewhat slower to process all voxels: depends
on the size of the ROI
10
Local Rigid Prostate Registration
Conebeam CT
scans
Delineated
contour
Conventional
planning CT scan
Delineated contour
+ 5 mm margin
Masked
planning CT scan
Automatic 3D
grey value
registration
Smitsmans et al.,IJROBP 2004
Automatic prostate localization in CBCT
(30 s)
Cone beam CT
10 CBCT scans: automatic bone match
Planning CT contours
placed automatically
10 CBCT scans: automatic prostate match
help line (GTV+3.6 mm)
Smitsmans et al., IJROBP 2004, 2005
Image Guided
Correction Strategies
11
Image Guided Radiotherapy
• Image the tumor + organs-at-risk or their
surrogates just prior or during treatment
• Assess changes in patient position relative to
treatment plan
• Adapt treatment plan (couch shift) to account for
changes, increasing treatment precision
The modern radiotherapy process
Pre-treatment Imaging
Treatment Planning
Treatment Delivery
In Room Imaging
Image Registration
& Correction
Dosimetry
Image Analysis: comparing with
reference image
Reference-Verification image
Reference Image Verification image Color-fused image
(unmatched)
(conventional CT) (cone beam CT)
12
Image Registration
Reference image
Verification image
Required couch shift:
(-3.2, -1.5, -0.6) mm
Stine Korreman
6 degrees of freedom couch
Literature
•
Guckenberger et al. Precision of image-guided radiotherapy (IGRT)
in six degrees of freedom and limitations in clinical practice.
Strahlenther Onkol. 2007 Jun;183(6):307-13
→ Reported 0.6 mm compensating translation per degree rotation
for non-immobilized patients
•
Linthout et al. Assessment of secondary patient motion induced by
automated couch movement during on-line 6 dimensional
repositioning in prostate cancer treatment. Radiother Oncol. 2007
May;83(2):168-74.
→ Reported negligible secondary motion, but did not correlate the
motion to the amount of rotation
13
Organ Motion
Organs move
from day to day
Couch shift in the presence of
Rotations
Just optimizing translations in
registration process
Couch shift driven by surrogates,
not by clinical rationale
Couch shift in the presence of
Rotations
Top
Middle
Base
14
Pop-Quiz #2
How many degrees of freedom are typically
used for IGRT image registration?
19%
20%
20%
22%
20%
1.
2.
3.
4.
5.
0
3
6
42
Not enough
Pop-Quiz #2
How many degrees of freedom are typically
used for IGRT image registration?
1.
2.
3.
4.
5.
0
3
6
42
Not enough
3) Van Herk et al. Seminars in
Radiation Oncology, 2007
Temporal Resolution
15
3D versus 4D CBCT
• 4D Data set
• 8 x 84
projections
• 3D Data set
• 670 projections
ROI by GTV Expansion
4D CBCT + GTV Contour
16
Local Rigid Body Registration
Visual Validation
Apply Correction
17
Concurrent
VMAT –
CBCT
acquisition
No MV-Beam
With MV- Beam
Validation scan during first VMAT arc
This amount of intra-fraction motion is rare
Validation scan during 2nd VMAT arc
18
DTS over which arc length?
This image cannot currently be display ed.
This image cannot currently be display ed.
10o
30o
10o
30o
50o
70o
50o
70o
Larger arcs give more information in the 3rd dimension, but require longer to acquire
Here we choose 30o arcs with limited out-of –plane information
Typical 30o DTS data
green=monitor, purple=verification
Rotating coordinate system
Tranverse
Errors are rare test method with localization scan as reference
Visual appearance of only actual patient
movement in the 6 patients studied
This image cannot currently be display ed.
Arc 1 No patient motion
(< 1 mm)
Arc 2 patient motion
(4 mm CC shift)
Detectable after 7% fraction dose
19
Fixating tumor position relative to treatment beam
Linac
“Safety margins
incorporating motion”
-static beam
-static couch
-wide beam
-100% duty cycle
Linac
“Dynamic couch
compensation”
-static beam
-dynamic couch
-small beam
->90% duty cycle
Linac
“Gating”
-static beam
-static couch
-small beam
-20-30% duty cycle
“Tracking/Pusuit”
Linac
-dynamic beam
-static couch
-small beam
->90% duty cycle
Courtesy of Tom Depuydt
Tumor tracking
Beam tracking (chasing) technologies
Courtesy of Tom Depuydt, Uwe Ölfke
The gimbaled moving beam in action …
Writing “UZB” with the 6 MV beam in a moving
GafChromic film with gimbals pan/tilt movements
Moving gimbaled
X-ray head
Tracked IR marker
(3x FFW)
VERO system UZ Brussel, 2010
Courtesy of Tom Depuydt
20
Vero DT: Hybrid approach with external IR markers
“stable” IR markers
Acquisition of kV
fluoro sequence
(20,30 or 40s) and
IR marker motion
“moving” IR markers
tumor and implanted
Visicoil
1
Detection Visicoil
and Building
correlation model
(IR vs internal
motion)
Courtesy of Tom Depuydt
Bas Raaymakers: UMC
1D MRI signal
1D MRI, Navigator echos (NE)
15 ms per acquisition
Time
Monitoring breathing at superior
side of liver
• In diagnostics
used to track/gate
respiration
• Imaging stack is
moved according
to NE signal
• Diaphragm
monitored
• Can be positioned
anywhere in any
orientation
Patient specific QA: EPID imaging for each DT fraction
beam 1
Visibility in some frames of tumor and implanted fiducial marker
beam 7
beam 2
beam 3
“The proof of the pudding ...”
beam 4
Courtesy of Tom Depuydt
21
Matthias Guckenberger
Motion compensation techniques
CC
Guckenberger et al. Radiother Oncol 2009
3D
• Large margins for stereotactic positioning and EPID based IGRT
• Imaging of pulmonary tumor with online correction of errors reduced
margins most effectively
• Small benefit of real-time correction of intra-fractional base-line drifts
• Limited benefit of gated beam delivery for tumor motion <15mm
Library of Plans
Toxicity Reduction by Online Adaptive Radiotherapy
Box Technique
Goal: Small-Margin IMRT
Challenge: Daily Target Motion
ESTRO IGRT 2011
Mischa Hoogeman
22
Plan Library Construction
1. Create Plan Library by Individualized
Motion Model
A novel individualized online
adaptive treatment strategy for
cervical cancer patients based on
pre-treatment acquired variable
filling CT-scans", by L. Bondar, M.
Hoogeman, J-W. Mens, S. Quint,
R. Ahmad, G. Dhawtal, B. Heijmen,
International Journal of Radiation
Oncology Biology Physics,
accepted (2011)
Mischa Hoogeman
ESTRO IGRT 2011
Toxicity Reduction by Online Adaptive Radiotherapy
1. Daily Plan Selection by In-Room Cone
Beam CT Imaging
2. Verification of Primary Tumor by
Implanted Markers
Mens JW, Quint S et al. 2011
Mischa Hoogeman
ESTRO IGRT 2011
Pop-Quiz #3
A library of plans is most suitable to correct
for
19%
23%
19%
21%
18%
1.
2.
3.
4.
5.
Respiratory motion
3D Setup error
Tumor regression
3D Organ motion
1D Organ deformation
23
Pop-Quiz #3
A library of plans is most suitable to correct
for
1.
2.
3.
4.
5.
Respiratory motion
3D Setup error
Tumor regression
3D Organ motion
1D Organ deformation
5) Bondar et al. Int J Radiat
Oncol Biol Phys. 2012
Beyond the Obvious
Differential Motion and Shape
Variabilty
Planning CT
4D-CBCT
No couch correction can solve this problem
CTV
24
Changes in Motion and
Regression
The modern radiotherapy process
Pre-treatment Imaging
Treatment Planning
Treatment Delivery
In Room Imaging
Image Registration
& Correction
The Adaptive Replanning Process
Pre-treatment Imaging
Treatment Planning
Treatment Delivery
In Room Imaging
Adaptive Replanning
Image Registration
& Correction
Treatment Assessment
25
Jaffray / PMH
Adaptive Radiotherapy
Real time
On-line
Off-line
Temporal Scales of Intervention
26