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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

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Introduction

Many In-room Imaging Systems

Multimodality Images

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Adaptive RadiotherapyAdaptive RadiotherapyJaffray / PMHJaffray / PMH

Temporal Scales of InterventionTemporal Scales of Intervention

Real timeReal time Off-lineOff-lineOn-lineOn-line

‘Adaptive’ Radiotherapy‘Adaptive’ Radiotherapy

Setup Errors

The patient moves from day to day

Organs move from day to day

Organ Motion

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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

22%

20%

20%

19%

19%

What is the purpose of IGRT?

Pop-Quiz #1

1. Make pretty images

2. Minimize setup error

3. Quantify organ motion

4. Reduce PTV margins

5. Sell more expensive treatment machines

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1. Make pretty images

2. Minimize setup error

3. Quantify organ motion

4. Reduce PTV margins

5. Sell more expensive treatment machines

What is the purpose of IGRT?

Pop-Quiz #1

4) Seminars in Radiation Oncology Volume 17, Issue 4

Quantification of

Organ Motion

Repeat Contouring

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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 correspondencesbetween imaging data sets (2D/3D/4D) that differ in time, space, modality and/or subject

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What is an Image

An image is a N-dimensional mathematical function mapping coordinates to intensity values

Principle of Image Registration

Floating Image

Fixed Image

InterpolatorInterpolator TransformerTransformer

Degrees of Freedom

FewFew ManyManyNone ?None ?

PET/CTPET/CT MR - CTMR - CT 4D CT4D CT

3 xN3 xN3 to 63 to 60?0?

Marc Kessler / UMMarc Kessler / UM

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(local) Rigid registration in 3D:• 3 Translations• 3 Rotations

6 Degrees of Freedom (DOF)e.g. Couch corrections

Transformations

Translations Rotations Scaling Shearing

Non Affine

General Framework for Image Registration

Fixed image

Floating image

Geometric Transformation

Mapped Image

MetricMetric

TransformerTransformerInterpolatorInterpolator

SimilarityOptimizerOptimizer

AdjustedParameters

“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

Possible images or scans

Floating image is manipulated during image registration operation (arbitrary choice)

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General Framework for Image Registration

Fixed image

Floating image

Geometric Transformation

Mapped Image

MetricMetric

TransformerTransformerInterpolatorInterpolator

SimilarityOptimizerOptimizer

AdjustedParameters

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

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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 matchingUses all pixel values in ROI: e.g., sum of squared differences

Somewhat slower to process all voxels: depends on the size of the ROI

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Local Rigid Prostate Registration

Delineated contour + 5 mm margin

Delineated contour

Automatic 3D grey value registration

Masked planning CT scan

Conventional planning CT scan

Cone-beam CT scans

Smitsmans et al.,IJROBP 2004

Automatic prostate localization in CBCT

(30 s)

Cone beam CT

Planning CT contours

placed automatically

10 CBCT scans: automatic bone match

10 CBCT scans: automatic prostate match

help line (GTV+3.6 mm)

Smitsmans et al., IJROBP 2004, 2005

Image Guided

Correction Strategies

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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 processPre-treatment Imaging Treatment Planning

In Room Imaging Image Registration& Correction

Treatment Delivery

Dosimetry

Image Analysis: comparing with

reference image

Reference Image(conventional CT)

Verification image(cone beam CT)

Color-fused image(unmatched)

Reference-Verification image

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Image Registration

Required couch shift: (-3.2, -1.5, -0.6) mm

Reference image Verification image

6 degrees of freedom couchStine KorremanStine Korreman

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

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Organs move from day to day

Organ Motion

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

Base

Middle

15

20%

22%

20%

20%

19%

How many degrees of freedom are typically used for IGRT image registration?

Pop-Quiz #2

1. 0

2. 3

3. 6

4. 42

5. Not enough

1. 0

2. 3

3. 6

4. 42

5. Not enough

How many degrees of freedom are typically used for IGRT image registration?

Pop-Quiz #2

3) Van Herk et al. Seminars in Radiation Oncology, 2007

Temporal Resolution

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3D versus 4D CBCT

• 4D Data set• 8 x 84 projections

• 3D Data set• 670 projections

ROI by GTV Expansion

4D CBCT + GTV Contour

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Local Rigid Body Registration

Visual Validation

Apply Correction

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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

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DTS over which arc length?

This image cannot currently be displayed.This image cannot currently be displayed.

10o 30o

50o 70o

10o 30o

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 datagreen=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

Arc 1 � No patient motion(< 1 mm)

Arc 2 � patient motion(4 mm CC shift)

Detectable after 7% fraction dose

This image cannot currently be displayed.

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Fixating tumor position relative to treatment beam

Linac Linac

LinacLinac

“Safety marginsincorporating motion”

“Gating”

“Dynamic couchcompensation”

“Tracking/Pusuit”

-static beam-static couch

-wide beam-100% duty cycle

-static beam-static couch

-small beam-20-30% duty cycle

-static beam-dynamic couch

-small beam->90% duty cycle

-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

Writing “UZB” with the 6 MV beam in a movingGafChromic film with gimbals pan/tilt movements

Moving gimbaled X-ray head

Tracked IR marker

(3x FFW)

The gimbaled moving beam in action …

VERO system UZ Brussel, 2010Courtesy of Tom Depuydt

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Vero DT: Hybrid approach with external IR markers

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Acquisition of kV fluoro sequence

(20,30 or 40s) andIR marker motion

Detection Visicoil and Building

correlation model (IR vs internal

motion)

“stable” IR markers“moving” IR markers

tumor and implanted Visicoil

Courtesy of Tom Depuydt

1D MRI, Navigator echos (NE)15 ms per acquisition

Time

1D

MR

I sig

na

l

• In diagnostics used to track/gate respiration

• Imaging stack is moved according to NE signal

• Diaphragm monitored

• Can be positioned anywhere in any orientation

Monitoring breathing at superior side of liver

Bas Raaymakers: UMCBas Raaymakers: UMC

beam 1 beam 7beam 2

beam 3beam 4

Visibility in some frames of tumor and implanted fiducial marker

“The proof of the pudding ...”Patient specific QA: EPID imaging for each DT fraction

Courtesy of Tom Depuydt

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• 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

CC3D Guckenberger et al. R

adiotherO

ncol2009

Motion compensation techniquesMatthias GuckenbergerMatthias Guckenberger

Library of Plans

Toxicity Reduction by Online Adaptive Radiotherapy

Box Technique Goal: Small-Margin IMRT

Challenge: Daily Target Motion

Mischa HoogemanMischa HoogemanESTRO IGRT 2011

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1. Create Plan Library by Individualized

Motion Model

Plan Library Construction

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 HoogemanMischa Hoogeman ESTRO IGRT 2011

2. Verification of Primary Tumor by

Implanted Markers

1. Daily Plan Selection by In-Room Cone

Beam CT Imaging

Toxicity Reduction by Online Adaptive Radiotherapy

Mens JW, Quint S et al. 2011

Mischa HoogemanMischa Hoogeman ESTRO IGRT 2011

18%

21%

19%

23%

19%

A library of plans is most suitable to correct for

Pop-Quiz #3

1. Respiratory motion

2. 3D Setup error

3. Tumor regression

4. 3D Organ motion

5. 1D Organ deformation

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1. Respiratory motion

2. 3D Setup error

3. Tumor regression

4. 3D Organ motion

5. 1D Organ deformation

A library of plans is most suitable to correct for

Pop-Quiz #3

5) Bondar et al. Int J Radiat Oncol Biol Phys. 2012

Beyond the Obvious

Differential Motion and Shape

Variabilty

No couch correction can solve this problem

Planning CT

4D-CBCT

CTV

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Changes in Motion and

Regression

The modern radiotherapy processPre-treatment Imaging Treatment Planning

In Room Imaging Image Registration& Correction

Treatment Delivery

The Adaptive Replanning ProcessPre-treatment Imaging Treatment Planning

In Room Imaging Image Registration& Correction

Treatment Delivery

Adaptive Replanning Treatment Assessment

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Adaptive RadiotherapyAdaptive RadiotherapyJaffray / PMHJaffray / PMH

Temporal Scales of InterventionTemporal Scales of Intervention

Real timeReal time Off-lineOff-lineOn-lineOn-line