what is in-room image-guidance? why in-room image … a. jaffray, kamal chawla, cedric yu, john w....

5/2/2011

1

The Use of In-room kV Imaging for IGRT

John W. Wong, Johns Hopkins University

David Jaffray, Princess Margaret Hospital

Fang-fang Yin, Duke University

ACMP 2011_jww

Disclosure

• The presenter has

– research agreement funded by Elekta

– financial interest in cone-beam CT technology

ACMP 2011_jww

Why In-Room Image-Guidance?

• To improve the targeting precision and accuracy so that treatment margin from CTV to PTV could be reduced

• Challenges:– uncertain about the target location– uncertain about the target shape– uncertain about the target motion– limitations of tools used for image-guidance

ACMP 2011_jww

What is In-room Image-Guidance?Use of imaging method in the treatment room while patient

stay at the treatment position

• To localize, monitor, and track surrogates which are associated to the patient and are of interest to radiation treatment

• To generate a list of choices for decision-making and intervention for positioning and modification

• To direct how the treatment couch or radiation beam should be modified

ACMP 2011_jww

5/2/2011

2

TG 104: The role of In-room KV imaging for patient setup and target localization

Fang-Fang Yin, Co-Chair, Duke University Medical CenterJohn Wong, Co-Chair, John Hopkins UniversityJames Balter, University of Michigan Medical CenterStanley Benedict, Virginia Commonwealth UniversityJean-Pierre Bissonnette, Princess Margaret HospitalTimothy Craig, Princess Margaret HospitalLei Dong, M.D. Anderson Cancer CenterDavid Jaffray, Princess Margaret HospitalSteve Jiang, Massachusetts General HospitalSiyong Kim, Mayo Clinic, JacksonvilleCharlie Ma, Fox Chase Cancer CenterMartin Murphy, Virginia Commonwealth UniversityPeter Munro, Varian Medical SystemsTimothy Solberg, University of Nebraska Medical CenterQ. Jackie Wu, Duke University Medical Center

* Gigas Mageras, Ellen YorkACMP 2011_jww

Objectives

1. Understand the challenges of treatment verification; leading to in-room kV imaging

2. Understand the configurations and operation principles of different in room kV x-ray imaging systems

3. Understand the requirements for effective implementation and quality assurance for IGRT

4. Understand the clinical applications and the associated limitations

ACMP 2011_jww

Evolution of in-room x-ray imaging in RT

In the 50’s – 60’s:

• A separate kV x-ray system and Cobalt-60 unit linked through a mobile couch (Karolinska University Hospital);

• A kV x-ray source attached to the beam stopper of a Cobalt-60 unit (Holloway 1958)

• A customized Cobalt-60 unit (Johns and Cunningham 1959) linear accelerator (Weissbluth,Karzmark et al. 1959)

• A Cobalt-60 unit and a kV x-ray tube mounted at 90o from each other on a circular ring (Netherlands Cancer Inst.)

• A Cobalt-60 unit with an x-ray tube mounted to the collimator at an offset angle (Shorvon, Robson et al. 1966)

ACMP 2011_jww

Ontario Cancer Institute's X-otron Cobalt-60 unit

kV x-ray source

kV Imaging on-board a cobalt-60 unit

ACMP 2011_jww

5/2/2011

3

• 70’s – 80’s --- The age of MV port film

– “Ready-pack” and film system for radiation therapy (Haus, Marks, Griem, 1973)

• 80’s ---- 45o

off-set kV x-ray source

– 10 MV medical accelerator at MGH (Biggs, et al. 1985)

– same screen/film system with MV beam (Shiu, 1987)

– RADII product by HRL Inc

• 80’s ---- The advent of electronic portal imaging (EPI)

– Renewed recognition of deficient MV image quality

ACMP 2011_jww

Evolution of in-room x-ray imaging in RT Challenges of Portal Imaging

• Quality difference between prescription kV images and treatment MV images

– May affect accuracy in error detection

• Deriving appropriate correction from EPID images

– Large residual error of correction using single projection, 20% > 5 mm

• Need for more projection and more repeat imaging

– Concerns of imaging dose (4-6 MU per film image)

• Lack of soft-tissue contrast

– uncertainty in the actual delivered dose

• kV in place of MV imaging offers a reasonable solution

ACMP 2011_jww

Absorption Unsharpness: kV vs MV

50kVp 6 MV100 kVp

ACMP 2011_jww

Absorption Unsharpness: kV vs MV

X Position (mm)

-15 -10 -5 0 5 10 15

Transm

ission (

scaled

to full r

ange)

0.0

0.2

0.4

0.6

0.8

1.0

Al

20mm

Detector (M=1.05)

6MV

100 kVp

50 kVp2 MeV

50 keV

30 keV

ACMP 2011_jww

5/2/2011

4

The era of in-room kV x-ray imaging in RT

90’s – present: Gantry mounted kV imaging

• Low-Z target to generate low energy MV x-rays for imaging (Galbraith 1989; Ostapiak, O'Brien et al. 1998)

• Integrated kV-MV x-ray target (Cho and Munro 2002)

• Gantry mounted 37o

offset kV/MV imaging system with image intensifier(Sephton and Hagekyriakou 1995)

• Gantry mounted kV/MV imaging system with EPID

– 45o offset (Jaffray, Chawla et al. 1995)

– 90o offset with CBCT capability (Jaffray et al. 1999).

– Precursor to modern commercial systems

ACMP 2011_jww

A little story – Dual Beam Imaging, 1995

DAVID A. JAFFRAY, KAMAL CHAWLA, CEDRIC YU, JOHN W. WONG.DUAL-BEAM IMAGING FOR ONLINE VERIFICATION OF RADIOTHERAPY FIELD PLACEMENT. Int. I. Radiation Oncology Biol. Phys., Vol. 33. No. 5. pp. 1273-1280, 1995

ACMP 2011_jww

ACMP 2011_jww

A little story: MV conebeam CT in 1995

• Paul Cho introduced CBCT algorithm (U Washington, 1993)

• Chang Pan manually acquired 90 projection images (6 MV)

– in room, rotate phantom, out of room, shoot and acquire

ACMP 2011_jww

Dual Beam Imaging on

Philips SL: 1996

Practicing on Bare Drum: Spring 1997

SL Mechanicals -under load

D. Jaffray R. CookeD. DrakeM.

Moreau

5/2/2011

5

ACMP 2011_jww

• April – May 1997, Two weekends, one month apart

• Wk 1: Drill holes, move electronics; Wk 2: Mount x-ray source and imager

Wood Cover

CCD EPID

The era of in-room kV x-ray imaging in RT

90’s – present: Room-mounted systems

• An in-room CT scanner with the medical accelerator (Akanuma, Aoki et al. 1984; Uematsu, Fukui et al. 1996)

• Wall/ceiling/floor - mounted multi-kV fluoroscopy systems

– Murphy and Cox 1996 -- Prototype CyberKnife)

– Schewe, Lam et al. 1998 -- Portable CCD-based imager

– Shirato, Shimizu et al. 2000 - 4 systems for gating RT

– Yin, Ryu et al. 2002 – BrainLab kV image guidance

ACMP 2011_jww

ACMP 2011_jww

The “Omni” in-room CT system

ACMP 2011_jww

In-room Conventional CT for IGRT

Memorial Sloan Kettering Cancer Center, 2003

5/2/2011

6

ACMP 2011_jww Curtsey of Lei Dong, Ph.D., MD Anderson Cancer Center, TX

Varian-GE ExaCTTM-on-Rails

Side rail to

provide

balance

Magnetic

encoder

strip

Central

guide rail

Fig. IIA.-3 There are three rails in this moving-gantry CT scanner. The central rail contains positional sensor and drive mechanism; and the two side rails provide level and balance during movement.

ACMP 2011_jww

helical scan:3 cm/s; scout scan: 7.5 cm/s

From C Ma

Curtsey of Lisa Grimm, Ph.D., Morristown Memorial Hospital, NJ.

Siemens Primatom system

ACMP 2011_jww

Siemens CT-on-Rails Ceiling/Floor-Mounted System

SDD: 3.62 mSID: 2.34 mPixel: 0.4 mmMatrix: 512x512

DigitalDetector

kV x-ray tube

F-F Yin Med Phy 2002

Novalissystem

ACMP 2011_jww

5/2/2011

7

Ceiling/Floor-Mounted System

Detector

X-ray tube X-ray tube

Recessed Detector

Curtsey of Accuray, Inc.

Detectors above the floor

Detectors under the floor

Cyberknife system

ACMP 2011_jww ACMP 2011_jww

Gantry-Mounted Systems

Elekta Synergy

Varian OBI

Siemens Artiste

kV Fluoroscopic, Radiographic, and CT Functionality

Radiographic Tomographic

Fluoroscopic

ACMP 2011_jww

The “Omni” Gantry System at Duke

Recessed ExactTract KV tube

KV DetectorVideo/IR Camera

OBI KV Detector

OBI KV tube

MV Detector

NovalisTx SystemDuke University Medical Center

ACMP 2011_jww

5/2/2011

8

ACMP 2011_jww

Acceptance Testing: Imaging System

• The primary goal for acceptance testing is to verify the components, the configurations, the functionality, the safety, and the performance of the system relative to the specifications described in the purchasing agreement and/or installation documentation from the vendors

• Data generated in the acceptance testing could be used as the baseline for routine QA

ACMP 2011_jww

ACMP 2011_jww

127.5

128.0

128.5

129.0

129.5

130.0

130.5

127.0 128.0 129.0 130.0

T-G

Dir

ection, Y

Axi

s,

mm

X Axis in A-B Direction, mm

Exp CW

Exp CCW

Adjusted points

Adjusted circle

Couch shift

126.5

127.0

127.5

128.0

128.5

129.0

129.5

127.0 128.0 129.0 130.0

T-G

Dir

ection, Y

Axi

s,

mm

X Axis in A-B Direction, mm

Exp CW

Exp CCW

Adjusted points

Adjusted circle

Couch shift

Dia = 0.6 mmDia = 2.5 mm

Before After

Acceptance: Synergy Table Axis “Tuning”TG142 : +/- 1mm

ACMP 2011_jww

5/2/2011

9

Integrated CT/Linac: Mechanical precision and alignment uncertainty

(Court, et al, MDACC)

ACMP 2011_jww

Fiducial Transfer Method

ACMP 2011_jww


5/2/2011

10

Acceptance Testing: Gantry Imaging System

• Room design and shielding consideration

• Verification of Imaging System Installation

• Safety and Mechanical Configurations

– System interlocks

– kV imaging arm movement

• Geometric Calibration

• Localization Accuracy

• Image Quality

ACMP 2011_jww

Elekta XVI system

• 2D Imaging system checks

– 2D low contrast visibility (0.9%)

– 2D spatial resolution (1.8 lp/mm)

• 2D geometric accuracy

– kV localization of MV isocenter from different gantry

– specification < 4 pixel, 1.04 mm

• ave. 1.5 pixels, max 3 pixel

ACMP 2011_jww

Leeds TOR 18FG

Elekta XVI Acceptance (Baseline)

• 3D imaging system checks

– Uniformity

– Low Contrast visibility

– Spatial Resolution

– Transverse vertical/horizontal scale

– Sagittal geometric

• 3D registration accuracy

ACMP 2011_jww

Elekta/Varian: 3D spatial resolution

TrueBeam image courtesy of Peter Munro

9

11

1315

9

11

1315

ACMP 2011_jww

5/2/2011

11

Elekta XVI Acceptance (Baseline)

• 3D imaging system checks

– Uniformity: 1.1%

– Low contrast visibility (polystyrene – LDPE, 1.26%)

– Spatial resolution (12 lpcm)

– Transverse vertical/horizontal scale (as expected)

– Sagittal geometric (as expected)

• 3D kV-MV registration accuracy

– < 1 mm as specified

ACMP 2011_jww

Quality Assurance Programs

• Safety and functionality

• Geometric accuracy

• Dosimetric information

• Software and hardware

• Imaging system with delivery system alignment/coincidence

• Image quality

• TG 142 sets the frequencies and criteria

ACMP 2011_jww

ACMP 2011_jww * Recommendations for Imaging System QA

Procedure non-SRS/SBRT SRS/SBRT

Daily


Procedure non-SRS/SBRT SRS/SBRT

Monthly

5/2/2011

12


Annual

Procedure non-SRS/SBRT SRS/SBRT Dose/Exposure vs Imaging Modality

Murphy et al Med Phys 2007 TG 76 Report

ACMP 2011_jww

Calibration for Ceiling/floor-Mounted System (ExacTrac System)

Isocenter calibration phantom x-ray calibration phantom


5/2/2011

13

QA for OBI/CBCT

• Safety and functionality

– Interlocks, lights, network-flow.

– All test items are verified during tube warm-up (< 5 min)

• Geometric accuracy

– OBI isocenter accuracy

– Accuracy of performance for 2D-2D match and couch shift

– Mechanical accuracy (arm positioning of KVS and KVD)

– Isocenter accuracy over gantry rotation

• OBI Image quality

– Radiography: contrast resolution and spatial resolution

– CBCT: HU reproducibility, contrast resolution, spatial

resolution, HU uniformity, spatial linearity, and slice thickness.

ACMP 2011_jww

1. MV Localization (0o) of BB;

collimator at 0 and 90o

qg-180 +180

u

v

qg

Reconstruction

qg

2. Repeat MV localization of BB for

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

3. Adjustment of BB to treatment

isocenter

4. Measurement of BB location in kV

radiographic coordinates (u,v) vs. qg.5. Analysis of ‘Flex Map’ and

storage for future use

6. Use ‘Flex Map’ during routine

clinical imaging

+1mm

-1mm

MV-kV calibration --- Elekta

XVI1

XVI2

XVI3

XVI4

XVI5

26 cm CW

26 cm CCW

40 cm CW

40 cm CCW

50cm CW

50 cm CCW

FOV:Rot. Dir:

Flex Maps: Synergy (XVI) Units

ACMP 2011_jww

-150 -100 -50 0 50 100 150-0.1

-0.05

0

0.05

0.1

U [

cm]

mean

+/- 2

-150 -100 -50 0 50 100 150-0.1

-0.05

0

0.05

0.1

Gantry angle [o]

V [

cm]

Long term stability for one unit (NKI)

u

v

6 calibrations

over 15

month period

Weekly QA of MV/kV isocenter calibrationACMP 2011_jww

5/2/2011

14

ACMP 2011_jww

All Flex Maps: Synergy (XVI) Units

ACMP 2011_jww

OBI1 Approach – “Residual”

Accept if within specified tolerance.

ACMP 2011_jww

Daily Geometry QA

• Align phantom with lasers

• Acquire portal images (AP & Lat) & assess central axis

• Acquire CBCT

• Difference between predicted couch displacements (MV & kV) should be < 2 mm

ACMP 2011_jww

Daily Geometry QA

• Align phantom with lasers

• Acquire portal images (AP & Lat) & assess central axis

• Acquire CBCT

• Difference between predicted couch displacements (MV & kV) should be < 2 mm

5/2/2011

15

Full kV/MV Calibration - Monthly



5/2/2011

16

ACMP 2011_jww

Compare Portal Image & DRR

ACMP 2011_jww

Iso _kV

Iso _OD I = Q /A P h an to m = L asers /OD I

Iso _M V

M V R ad iatio n

Iso cen ter

M V M ech an ica l

Iso cen ter

M V N o m im al

Iso cen ter

x

z

y

E 1 (EP ID’s)

E 2 (CBCT )

E 3

Current* Action Level on E3: 2 mm (in any one direction)

* Due to large observer variability in MV alignment

ACMP 2011_jww

2006 XVI Daily QA Results (E3 Error)

XVI1 XVI2 XVI3 XVI4 XVI5

[mm] L/R S/I A/P

M (-0.04, -0.72, 0.52)

Ave(σ) (0.96, 0.82, 1.04)

~ 6 Months of Daily QA Testing ACMP 2011_jww

2007 OBI Daily QA Results (E3 Error)

OBI1 OBI2 OBI3 OBI4

[mm] L/R S/I A/P

M = (-0.08, -0.19, 0.27)

Ave(σ) = (0.51, 1.02, 0.71)

5/2/2011

17

ACMP 2011_jww

CBCT: Geometric Accuracy and Precision

CBCT vs Orthogonal Portal Images

Phantom - Unambiguous Object

40 measurements over several months

Elekta Synergy RP

Sharpe et al. - Med Phys. 2006 Jan;33(1):136-44. ACMP 2011_jww

IG Performance:Connectivity,Orientation/Scale Checks

CT

Simulation

Treatment Planning System

XVI

Acquisition

OBI

Acquisition

Off-line Image

Review/Archive

On-line Images

Planning CT‟s

DIC

OM

/RT

Volumetri

c

Refere

nce

Images

DICO

M/R

T

Image Source: GE and Philips CT Planning: Philips Pinnacle v7.4

ACMP 2011_jww

• Anthropomorphic phantom• 4 Orientations• Target bony anatomy • Arbitrary initial shifts• Plot residual error• 5 XVI units

Residual Error


ACMP 2011_jww

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

1

Re

sid

ua

l A

bso

lute

Err

or

[cm

]

.

.

L/R

S/I

A/P

All XVI‟s


5/2/2011

18

Baseline CBCT Imaging

ACMP 2011_jww

Affects

•How often can you scan

•Resolution

•Contrast/dose – thick patients

•Image homogeneity

•Noise

•Size

•Resolution

•Angular sampling

•Image homogeneity / noise

•Speed

•Resolution

X-ray source:

•Heat capacity

•Focal spot size

•Energy range

•Bow-tie filter

Flat-panel detector

•Quantum efficiency

•Size

•Resolution

•Speed

•Scatter grid

Gantry

•Speed

•Accuracy (constancy)

Bow-Tie Filter

• Reduce Scatter

• Lower Skin Dose

• Reduce Saturation

30 mm

2 mm

Aluminum

ACMP 2011_jww

Application of a Bow-Tie FilterBow-TieNo Bow-Tie

Central dose 3 cGy, skin 4 cGy Central dose 3 cGy, skin 3 cGy

2 minutes scan timeACMP 2011_jww

Effect of size (scan length) on image quality

1 mm2 voxels, 1 mm slice

thickness, 32 mA, 40

ms, 120 kV, 1.5 cGy

2 cm 12 cm

20 cm

ACMP 2011_jww

5/2/2011

19

Speed matters

• Number of projection images affects streak artifacts

• Given the IEC limit of 1 RPM

– Varian: 360 images for fast scan

– Elekta: 180 images for fast scan

• How much do you need?

– This depends on the task

ACMP 2011_jww

Which dose to use?

0.25 cGy 0.5 cGy

1 cGy 2 cGy

1 mm2 voxels, 1 mm slice thickness, 120 kVACMP 2011_jww

Dose Projections Translation (mm) Rotation (dg)

L-R C-C A-P L-R C-C A-P

3.0 cGy 640 -0.4 -2.3 -2.4 -1.0 0.1 0.3

0.3 cGy 64 -0.4 -2.4 -2.5 -1.0 0.0 0.3

0.1 22 -0.4 -2.4 -2.4 -0.9 0.1 0.3

0.1 cGy3.0 cGy 0.3 cGy

ACMP 2011_jww

Scatter grid

• Scatter grid attenuates

– + Scatter

– - Primary beam

• Software correction may be equally effective

ACMP 2011_jww

5/2/2011

20

Scatter correction algorithms

Elekta: scatter uniform and proportional to average image

intensity where there is patient in the beam

Boellaard et al. Two-dimensional exit dosimetry using a liquid-

filled electronic portal imaging device and a convolution model

Radiother. Oncol. 44 149-157, 1997

Without correction With correction

Varian TrueBeam: iterative kernel based scatter estimation

ACMP 2011_jww

Reconstruction settings

• Slice thickness

• Pixel size

• Pre-filtration

• Interpolation

• Reconstruction filtration

ACMP 2011_jww

1 mm slice thickness

Slice Thickness: 1 mm2 voxels, 20 mA, 20 ms, 120 kV, 1 cGy



ACMP 2011_jww

1 mm slice

thickness

5 mm slice

thickness,averaged

in all directions

ACMP 2011_jww

5/2/2011

21

PIXEL SIZE: 32 mA, 40 ms, 120 kV, bowtie, 3 cGy

2 mm2 voxels, 2 mm slice thickness 1 mm2 voxels, 1 mm slice thickness

0.5 mm2 voxels, 0.5 mm slice thickness 0.5 mm2 voxels, 2.5 mm slice thickness ACMP 2011_jww

Elekta setting: smoothed

1 mm2 voxels, 1 mm slice thickness, 32 mA, 40 ms, 120 kV, bowtie, 3 cGy

ACMP 2011_jww

Un-smoothed

ACMP 2011_jww

Patient Dose Estimation: kV-CBCT

• Beam Quality: HVL (kVp, filtration)

• Tube output: Reference (mR/ mAs)

• Scanning Geometry: SAD, FOV, No. of projections

• Technique settings: mAs

• Patient Size (Body , Head…)

Dose depends on

AAPM’10

Bench top CBCT System

5/2/2011

22

ACMP 2011_jww

CBCT: Radial Dose

0 2 4 6 8

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

Dos

e (

cGy)

Depth (cm)

FOV: 5 cm x 26cm

FOV: 10 cm x 26cm

FOV: 15 cm x 26cm

FOV: 26 cm x 26cm

Phantom: 16 cm dia.

Imaging Technique:

100 kVp

100 mA

20 ms

330 Projection

660 mAsDepth

ACMP 2011_jww

CBCT: Radial Dose

0 2 4 6 8 10 12 14

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

Dos

e (c

Gy)

Depth (cm)

FOV: 5 cm x 26cm

FOV: 10 cm x 26cm

FOV: 15 cm x 26cm

FOV: 26 cm x 26cm

Phantom: 30 cm dia.

Imaging Technique:

120 kVp

100 mA

20 ms

330 Projection

660 mAsDepth

Clinical Imaging Dose Measurements

A simple and clinical feasible method to estimated the CBCT imaging dose

Detectors Detectors

Kim et al,

Radiat Prot Dosi. 2008


0

0.5

1

1.5

2

0 10 20 30

Tota

l Do

se (

cGy)

Field Size (z) (cm)

Dcenter

D2cm

CBCT Imaging Dose: Offset Geometry (FOV 40 cm)

Experimental Setup Dose vs. Field Size

Nuclear Enterprises Free-Air Chamber (0.6 cc)

32 cm “Body” Phantom330 projections at 2 mAs / proj

Islam et al., Med. Phys. 2006

5/2/2011

23

mA

s/ P

roje

ctio

n

Number of Projections

2

1

0.5

80 160 320

Variation of image quality with lens dose (cGy)

4.02.01.0

0.5 1.0 2.0

0.25 0.5 1.0

Deciding the Necessary Image Quality for the Application

16x Reduction


Low Dose (1.5 mGy) Pediatric Imaging for Routine On-line IGRT

Artifacts in kV CBCT

• Cupping and streaks due to hardening and scatter (A&B)

• Gas motion streak (C)

• Rings in reconstructed images due to dead or intermittent pixels (D)

• Streak and comets due to lag in the flat panel detector (E)

• Distortions (clip external contours and streaks) due to fewer than 180 degrees + fan angle projection angles (F)


IGRT is Clinical Quality Assurance

• Provides measurement of patient position in treatment position.

– Quantitative, accurate, repetitive

– Minimally invasive

– Large field-of-view

– Markers, bone, soft-tissue, skin-line

• Verify consistency of planned and actual geometry

– Provides a critical data source for rational margin design

5/2/2011

24

MV vs kV Fallacy

• Daily orthogonal open-field MV/kV projection imaging; 14 patients

• Alternate week kV- vs MV-based correction

• Verify correction with kV orthogonal pair

• MV and kV correction similar with adequate anatomic information

• Appreciable rotation uncertainty

• Main kV advantage: reduced imaging dose

ACMP 2011_jww

H&N LungH&N Lung Pelvic

Off-Line In-Room Image-Guidance

Reference images

Patient setup

Correction?

Treatment

Ynth treatment

On-board images

Patient planning information/Patient information system

N

StatisticalAnalysis (m,)

In-room imaging

ACMP 2011_jww

On-Line In-room Image-Guidance

Reference imagesPatient setup

Correction? TreatmentN

Correct position

Y

Feedback

In-room imaging III In-room imaging II

In-room imaging I

Patient planning information/Patient information system

On-board images


Data: 1

Generic Margin

~ 2.5S + 0.7

Conventional RT

Data: n < N

Corrects for

systematic error

Off-line Adaptive RT

Data: daily

Corrects for all

setup/motion errors

On-line correction

Clinical IGRT Strategies:Margin --- from population to individual margin

• Key technologies for

quantifying treatment

uncertainties:

• Organ motion:

Computed

Tomography

• Daily setup:

Electronic Portal

Imaging

SI

Lat

5/2/2011

25

Adaptive Gating

ExacTrac IGRT

6D RoboticsFrameless Radiosurgery

Image-Guidance with ExacTrac

ACMP 2011_jww

Workflow Using Snap Verification

Initial 6D setup

Treat field 1 Treat field 2 Treat field 3

Snap verification for field 2



Treat field 4

....

ACMP 2011_jww

Use Case: Intra-Fraction Imaging

Example of dual x-ray imaging

ACMP 2011_jww

Image-Guidance with CT-on-Rails

Treatment

Room

Treatment Planning

Intranet

LINAC console

LINAC

Control Room

Alignment

Protocol

In-room

kV CT/CBCT

Images

Couch

Shifts

Gating

Signal

Planning and R&V System

Room

Reference CT

Reference

CT datasetImage

Storage

Imaging console

Correction?

R&V

System

Patient couch

ACMP 2011_jww

5/2/2011

26

Use Case – SBRT Pancreatic Cancer

• Collaborative randomized trial – Hopkins, Stanford, MSKCC

• 2-3 mm PTV expansion

• Implanted markers for visualization

• Hopkins: Breath-hold (ABC) planning CT to immobilize motion

• Setup: Compare free breathing planning CT with CBCT

• Treatment

– free breathing fluoroscopy of markers to verify motion

– kV projection to verify ABC-moderate deep inspiration- setup

– breath-hold kV projection imaging to verify markers’ positions during treatment

ACMP 2011_jww

ABC-kV AP setup

ABC-kV lateral setup kV intra-fx monitor at one beam angle

5/2/2011

27

Planning CT with target contours

Use Case: 3-D Free-Breath ITV with CBCT

CBCT images prior to correctionCBCT images after correctionPost-treatment CBCTWang et al Ref J 2007

ACMP 2011_jww

Au markers validation: MV vs. kV shift difference

MV with Markers CBCT with Markers

• Independent Alignment Methods

• 16 patients (~250 fx)

• Duration: 6 months

• Unambiguous Surrogate (3 Au markers)

vs

Moseley et al. Int. J. Rad. Onc. Biol. Phys., 63, 2007ACMP 2011_jww

ACMP 2011_jww

Upper GI

21%

Lung

41%

Head and Neck

26%

Lymphoma

3%

Sarcoma

9%

Background

• The XVI system is linked to the Remote

Automatic Table Movement (RATM).

• The patient is shifted per the image-guidance

system via the remote couch interface.

• The stability of the system and residual error is

measured through verification scans acquired

following a table shift.

Methodology

• Collection Period Oct 19th „06 – Nov 17th „06

• Patients with repeat (verification) scans were

measured and matched using an Automatic

Algorithm

• 34 patients with 135 scans

Clinical “end-to-end” assessment of IGRT

W Li et al. J Appl Clin Med Phys. 2009 Oct 7;10(4):3056

Summary

The introduction of in-room kV imaging provides new opportunities to further improve treatment accuracy and precision. At the same time, it presents new challenges for its efficient and effective implementation.

Each in-room kV imaging method has its strengths and limitations. The user is well advised to match the clinical objective with the appropriate technology; or at least to apply the image guidance information to within the bounds of its validity:

imaging dose, field of view, sharpness vs contrast

ACMP 2011_jww

5/2/2011

28

ACMP 2011_jww

Summary

• Guidance documents are available to assist in the establishment of QA programs for IGRT technologies

• Published literature demonstrate that these systems can be accurate, precise, and reliable.

– Compare your results to others.

– Adapt upgrades --- high resolution panels

• Maintenance of IGRT performance is central to confidence in appropriate PTV margin.

• An integrated daily check for IG system consistency has been implemented into routine clinical use with a 15 minute time penalty.

Future considerations for in-room x-ray IGRT

• Need to analyze institutional data (4.5 TB in 4 machine-years)

– Margin specification, revised action level, frequency

• On-board CT/CBCT is a snap shot

– Soft tissue target localization remains challenging

– Dose concerns with intra-fraction x-ray monitoring

– Alternative solutions are needed

• EM transponders

• MRI-Linac

• Integrated on-board ultrasound imaging

• Motion artifacts are problematic

– 4D CBCT, Breath-hold CBCT

ACMP 2011_jww

ACMP 2011_jww

1a

CBCT system

US system

(a)_ (b)_ (c)_

Contrast Enhanced CBCT – OBI 1.4 with no breathing motion

Courtesy of Michael Lovelock and Josh Yamada MD; MSKCC

ACMP 2011_jww

5/2/2011

29

Summary

• Radiotherapy x-ray imaging systems have a wealth of tunable parameters – users can change these!

• Imaging dose and field of view should be set given the clinical requirements

• Image resolution and sharpness can be set according to preference, but increasing sharpness also increases noise

• For image guidance, a high resolution is not required -‘soft’ reconstructions offer slightly better soft tissue contrast

ACMP 2011_jww

Varian - Elekta

Parameter Varian Truebeam ElektaXVI4.5

Energy range 40-140 kV 70-150 kV

Bow-tie filter yes yes

Detector QE 60% (CsI) 60% (CsI)

Detector size 30 x 40 cm 40 x 40 cm

Pixel 197 mm 400mm

Frame rate used 11 fps 5.5 fps

Scatter grid yes no

ACMP 2011_jww

what is in-room image-guidance? why in-room image … a. jaffray, kamal chawla, cedric yu, john w....

Documents