1

Marc Kessler

The University of Michigan

Image Processing

for

Tx Planning

Act II

Planning

Jan-Jakob Sonke

Netherlands Cancer Institute

Image Processing

for

Tx Delivery

Act III

Delivery

AAPM 2011

Disclosure

• Our department has research contracts with:

• Elekta Oncology Systems

• Philips Radiation Oncology Systems

• Siemens Medical Solutions

• Our department licenses software to:

• Elekta Oncology Systems

Radiotherapy ProcedureAct I:

Tattoo, align and

scan patient

Act II:

Define the target

and design a

treatment plan

Act III:

Align patient on

machine on tattoos and

treat (many days)

Setup Errors

The patient moves from day to day

2

Organs move

from day to day

Organ Motion 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

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

Safety Margins

Verellen et al. Nature Reviews Cancer 2007

3

Many In-room Imaging Systems

Visualization

Visualization: Image Fusion

Reference Image Localization Image

Visualization: Sliding Window

4

Visualization: Overlay

Complementary color overlay clearly shows gross differences and local

differences provided adequate contrast

Visualization: Animation

Animation clearly shows local changes

Bone Registration Bone Registration

5

Pop Quiz

What is the purpose of IGRT

20%

21%

20%

20%

19% 1. Make pretty images

2. Minimize setup errors

3. Quantify organ motion

4. Reduce PTV margins

5. Sell more expensive treatment machines

Pop Quiz

What is the purpose of IGRT

a) Make pretty images

b) Minimize setup errors

c) Quantify organ motion

d) Reduce PTV margins

e) Sell more expensive treatment machines

Correct Answer: d)

Seminars in Radiation Oncology Volume 17, Issue 4

2D Image Guidance

Electronic Portal Imaging

6

Portal Image QualityImage quality is limited by:

• Projective nature of 2D

images

• Low DQE of EPIDs in MV

range

• Limited dose used for

imaging (ALARA)

• Limited contrast differences

of tissue in the MV range

Mostly limited to bony anatomy alignment

minimizing setup errors

Prostate Lung

A-P

Lat

.

Preprocessing: unsharp masking

Top-hat transform

Original image Binary top-hat enhanced image

Portal image analysis - 2D

Match field-edge Match anatomyReference image

Setup Error = Anatomy Match – Field-Edge Match

7

3D EPID Dose reconstruction

prostate VMAT plan

• Energy: 10 MV

• 243 frames

• delivery time: 96 s

EPID movie Dose per frame Accumulated dose

axial slice through isocentre

3D Image Guidance

MV/kV Coincidence

• Treatment and

imaging beams are

orthogonal

Jean-Pierre Bissonnette: PMH

kV/MV Calibration Concept

kV

BB (reconstruction

Isocentre)

MV radiation isocentre

MV mechanical

isocentre

x

y

z

Calibrated isocentre

Jean-Pierre Bissonnette: PMH

8

qgantry

4. Measure BB Location in kV

radiographic coordinates (u,v) vs. qgantry.

+180qgantry-180

u

v

5. Analysis of ‘Flex Map’ and Storage for

Future Use.

+1mm

-1mm

Reconstruction

qgantry

6. Employment of ‘Flex Map’ During

Routine Clinical Imaging.

1. MV Localization (0o) of BB; collimator

at 0 and 90o.

2. Repeat MV Localization of BB for

gantry angles of 90o, 180o, and 270o.

3. Analyze images and adjust BB to

Treatment Isocentre (± 0.3 mm)

Jea

n-P

ierr

e B

isso

nn

ett

e:

PM

H

Geometry: Flex calibration

MV Flex kV Flex

Geometry: Flex calibration

MV Flex kV Flex-200 -150 -100 -50 0 50 100 150 200

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

angle [°]

dis

pla

cem

en

t [c

m]

XG

(AB)

YG

(GT)

9

Geometric non-idealities (Flex)

2 mm panel shift Correctly Calibrated

How many Degrees of Freedom?

Few ManyNone ?

PET/CT MR - CT 4D CT

3 x N3 to 60 ?

Marc Kessler / UM

Requirements for IGRT

registration

• Fast and robust image registration

• Easy visual validation

• Registration result drives a couch shift

Rigid registration with 6 degrees of freedom is

a likely candidate

Automatic matching on region of

interest built-in in Synergy system

Tumor in top of neck Tumor in lower part of neckRequired table shift:

(-3.2, -1.5, -0.6) mmRequired table shift:

(+1.5, -3.2, -6.1) mm

reference localization reference localization

10

Rotations Rotations

Correction by Couch Shift Modify Rotation Point

11

Correction by Couch Shift Soft Tissue Guidance

Grey-value registration TAP / TCC / TLR / RAP / RCC / RLR

** Smitsmans et al.,

IJROBP 60 (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

Pop Quiz

How many degrees of freedom are typically used

for IGRT image registration

17%

16%

23%

20%

24% 1. 0

2. 3

3. 6

4. 42

5. Not enough

12

Pop Quiz

How many degrees of freedom are typically used

for IGRT image registration

a) 0

b) 3

c) 6

d) 42

e) Not enough

Correct Answer: c)

Van Herk et al. Seminars in Radiation Oncology, 2007

Clarity Sim

Ultrasound Guided RT (Clarity™)

Throughout Radiation Oncology Care Cycle

LinacSim

Clarity AFC Workstation Clarity Guide

Martin LaChaine: Elekta

Fra

nk

Ve

rha

eg

en

: M

aa

str

o

3DUS vs CT for breast seroma cavity

Frank Verhaegen: Maastro

Planning CT Daily US Fusion

13

Radiotherapy systems with

integrated MRI

MRI-Linac Utrecht

Courtesy of Bas Raaijmaakers

MRI-Co60 ViewRay

Courtesy of Jim Dempsey

1.5 T MRI accelerator for MRI guided RT

at UMC Utrecht

No impact of beam on MRI

Prototype MRI accelerator

Bas Raaymakers: UMC

Inter- and intra- fracation motion of cervix

Day to day variation

Bas Raaymakers: UMC

4D Image Guidance

14

Breathing Respiratory signal extraction

Vertical

derivative filter

Temporal

concatenation

Amsterdam shroud (2D image)

Horizontal

projection

[Zijp, ICCR, 2004]

[van Herk, ICCR, 2007]

RCCBCT 3D versus 4D CBCT

• 4D Data set

• 8 x 84

projections

• 3D Data set

• 670 projections

15

ROI by GTV Expansion 4D CBCT + GTV Contour

Local Rigid Body Registration Visual Validation

16

Apply Correction Impact of Respiratory Motion

on Dose Distribution

Planned distribution Delivered distribution

• Shift of the dose distribution due to

displacement of the mean tumor position

• Blurring of the dose distribution due to

breathing around the mean position

Planned dose distribution:

hypofractionated lung treatment 3x18 Gy

Realized dose distribution with daily IGRT

on tumor (no gating)

9 mm margin is adequate even with 2 cm intrafraction motion

2 cm

17

4D Liver MRIJim Dempsey / ViewRay

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

orientationMonitoring breathing at superior

side of liver

Bas Raaymakers: UMC

1D MRI navigators, monitoring breath hold

stability and on-set of breathing

Monitoring breath hold at inferior

side of liver

Time

1D

MR

I sig

na

l

Bas Raaymakers: UMC

Gated radiation on moving cart

• Cart in scanner bore, moving along FH-direction

• Motion by electric motor/crankshaft mechanism

• Sinusoidal/respiratory-like motion

• Radiation sensitive film to record dose

• Water phantom to track position

• 5x5 cm2 radiation beam, dose ~2Gy, in static situation T = 2.5 min.

Bas Raaymakers: UMC

18

Gated radiation delivery

Bas Raaymakers: UMC

Pop Quiz

Which motion management strategy has the

largest impact on the delivered dose:

20%

20%

20%

22%

18% 1. 4D Imaging

2. 4D Planning

3. 4D Delivery

4. 4D Image Guidance

5. The impact of respiration is over exaggerated

Pop Quiz

Which motion management strategy has the

largest impact on the delivered dose:

a) 4D Imaging

b) 4D Planning

c) 4D Delivery

d) 4D Image Guidance

e) The impact of respiration is over exaggerated

Correct Answer: d)

Guckenberger et al. Radiother. Oncol. 2009

Adaptive Radiotherapy

19

Differential Variability

No couch correction can solve this problem

Repeat 4D cone beam CT

Shows respiration, tumor shrinkage and baseline position variation

Anatomical Changes

Bony anatomy

registration

non-rigid registration

Fraction at day # 36

20

Results, volume change of target + OAR

Relative weight loss, neck radius and delineated volumes

0.40

0.50

0.60

0.70

0.80

0.90

1.00

1.10

0 5 10 15 20 25 30 35 40

treatment day

un

its

Neck

weight

CTV

PTV tot

Spinal cord

Parotid Li

Parotid Re

day CTV PTV Spinal cord Parotid Li Parotid Re t(s)

0 387 1051 20 31 21 -

1 381 1036 20 31 21 67

7 378 1035 20 32 21 120

14 373 1008 20 27 20 104

21 373 1012 20 28 19 55

28 344 969 21 23 17 141

36 315 916 20 18 15 155

Deformable Registration

0 0.2 0.4 0.6 0.8 1 1.2 1.40

0.2

0.4

0.6

0.8

1

Dose [% Dmax]

Vo

lum

e [%

]

CTV

PTV

Brain stem

Left parotid

Spinal cord

Oral Cavity

Applications – dose painting

Pre

-tre

atm

en

tM

id-t

rea

tme

nt

Treatment response

Prescription function

Robert Jeraj / UW

Summary

• Geometrical uncertainties limit the precision of

radiotherapy

• 2D,3D&4D image registration and guidance

increases the precision of RT allowing margin

reduction and dose escalation

• Adaptive RT further individualized treatment

delivery

21

Acknowledgements

Marcel van HerkPeter RemeijerJochem WolthausSimon van KranenSimon RitMonique SmitsmansAnton MansDavid JaffrayDoug MoselyMarc KesslerJean-Pierre BissonnetteRobert JerayFrank VerhaegenBas RaaymakersJim DempseyMartin LaChaine