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5/2/2011
Disclosure
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
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Why In-Room Image-Guidance?
•
• The presenter has
– research agreement funded by Elekta
– financial interest in cone-beam CT technology
To improve the targeting precision and accuracy so that
treatment margin from CTV to PTV could be reduced
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
• Challenges:
– uncertain about the target location
– uncertain about the target shape
– uncertain about the target motion
– limitations of tools used for image-guidance
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TG 104: The role of In-room KV imaging for
patient setup and target localization
Fang-Fang Yin, Co-Chair, Duke University Medical Center
John Wong, Co-Chair, John Hopkins University
James Balter, University of Michigan Medical Center
Stanley Benedict, Virginia Commonwealth University
Jean-Pierre Bissonnette, Princess Margaret Hospital
Timothy Craig, Princess Margaret Hospital
Lei Dong, M.D. Anderson Cancer Center
David Jaffray, Princess Margaret Hospital
Steve Jiang, Massachusetts General Hospital
Siyong Kim, Mayo Clinic, Jacksonville
Charlie Ma, Fox Chase Cancer Center
Martin Murphy, Virginia Commonwealth University
Peter Munro, Varian Medical Systems
Timothy Solberg, University of Nebraska Medical Center
Q. Jackie Wu, Duke University Medical Center
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* Gigas Mageras, Ellen York
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
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kV Imaging on-board a cobalt-60 unit
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)
kV x-ray source
Ontario Cancer Institute's X-otron Cobalt-60 unit
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Evolution of in-room x-ray imaging in RT
• 70’s – 80’s --- The age of MV port film
– “Ready-pack” and film system for radiation therapy
(Haus, Marks, Griem, 1973)
o
• 80’s ---- 45 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
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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
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Absorption Unsharpness: kV vs MV
Transmissio n (scaled to full range)
Absorption Unsharpness: kV vs MV
1
.
0
50kVp
100 kVp
6 MV
0
.
8
A
l
2
0
m
m
0
.
6
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o
r
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M
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1
.
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)
6
M
V
0
.
4
1
0
0
k
V
p
0
.
2
3
0
k
e
V
5
0
k
e
V
5
0
k
V
p
2
M
e
V
0
.
0
1
5
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1
0
5
0
5
1
0
1
5
X
P
o
s
i
t
i
o
n
(
m
m
)
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A little story – Dual Beam Imaging, 1995
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)
o
• Gantry mounted 37 offset kV/MV imaging system with
image intensifier(Sephton and Hagekyriakou 1995)
• Gantry mounted kV/MV imaging system with EPID
o
– 45 offset (Jaffray, Chawla et al. 1995)
– 90o offset with CBCT capability (Jaffray et al. 1999).
– Precursor to modern commercial systems
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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
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A little story: MV conebeam CT in 1995
Dual Beam
Imaging on
Philips SL: 1996
Practicing on Bare
Drum: Spring 1997
M.
Moreau
• 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
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D. Drake
D. Jaffray
R. Cooke
SL Mechanicals under load
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The era of in-room kV x-ray imaging in RT
Wood Cover
CCD EPID
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
•
•
April – May 1997, Two weekends, one month apart
Wk 1: Drill holes, move electronics; Wk 2: Mount x-ray source and imager
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In-room Conventional CT for IGRT
The “Omni” in-room CT system
Memorial Sloan Kettering Cancer Center, 2003
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Varian-GE ExaCTTM-on-Rails
Central
guide rail
Magnetic
encoder
strip
Side rail to
provide
balance
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Curtsey of Lei Dong, Ph.D., MD Anderson Cancer Center, TX
Fig. IIA.-3 There are three rails in this moving-gantry CT scanner. The central rail contains
helical scan:3 cm/s; scout scan: 7.5 cm/s
positional sensor and drive mechanism; and the two side rails provide level and balance
during movement.
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Ceiling/Floor-Mounted System
Siemens CT-on-Rails
Novalis
system
From C Ma
SDD: 3.62 m
SID: 2.34 m
Pixel: 0.4 mm
Matrix: 512x512
Digital
Detector
kV x-ray
tube
Siemens Primatom system
Curtsey of Lisa Grimm, Ph.D., Morristown Memorial Hospital, NJ.
F-F Yin Med Phy 2002
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Gantry-Mounted Systems
Ceiling/Floor-Mounted System
Varian OBI
Cyberknife system
X-ray tube
X-ray tube
Detector
Recessed Detector
Detectors under the floor
Elekta Synergy
Detectors above the floor
Siemens Artiste
Curtsey of Accuray, Inc.
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kV Fluoroscopic, Radiographic, and CT
Functionality
The “Omni” Gantry System at Duke
Video/IR Camera
KV Detector
NovalisTx System
Duke University
Medical Center
OBI KV
Detector
OBI KV tube
MV Detector
Recessed ExactTract
KV tube
Fluoroscopic
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Radiographic
Tomographic
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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
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Acceptance: Synergy Table Axis “Tuning”
TG142 : +/- 1mm
Before
After
Exp CW
Exp CCW
Adjusted points
Adjusted circle
Couch shift
130.5
T-G Direction, Y Axis, mm
129.0
T-G Direction, Y Axis, mm
130.0
129.5
128.5
129.0
128.0
128.5
127.5
128.0
127.0
127.5
127.0
128.0
129.0
X Axis in A-B Direction, mm
Dia = 2.5 mm
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Exp CW
Exp CCW
Adjusted points
Adjusted circle
Couch shift
129.5
130.0
126.5
127.0
128.0
129.0
X Axis in A-B Direction, mm
130.0
Dia = 0.6 mm
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Integrated CT/Linac: Mechanical precision and alignment uncertainty
(Court, et al, MDACC)
Fiducial Transfer Method
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Elekta XVI system
Acceptance Testing: Gantry Imaging System
• Room design and shielding consideration
• Verification of Imaging System Installation
• 2D Imaging system checks
– 2D low contrast visibility (0.9%)
– 2D spatial resolution (1.8 lp/mm)
• Safety and Mechanical Configurations
– System interlocks
– kV imaging arm movement
• Geometric Calibration
• Localization Accuracy
• Image Quality
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Leeds TOR 18FG
• 2D geometric accuracy
– kV localization of MV isocenter from different gantry
– specification < 4 pixel, 1.04 mm
• ave. 1.5 pixels, max 3 pixel
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Elekta/Varian: 3D spatial resolution
Elekta XVI Acceptance (Baseline)
• 3D imaging system checks
– Uniformity
– Low Contrast visibility
– Spatial Resolution
– Transverse vertical/horizontal scale
– Sagittal geometric
• 3D registration accuracy
15
15
13
13
11
11
9
9
TrueBeam image courtesy of Peter Munro
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Elekta XVI Acceptance (Baseline)
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
• 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
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Daily
Procedure
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non-SRS/SBRT
Monthly
SRS/SBRT
* Recommendations for Imaging System QA
Procedure
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non-SRS/SBRT
SRS/SBRT
* Recommendations for Imaging System QA
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Annual
Procedure
non-SRS/SBRT
SRS/SBRT
Dose/Exposure vs
Imaging Modality
Murphy et al
Med Phys 2007
TG 76 Report
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* Recommendations for Imaging System QA
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Calibration for Ceiling/floor-Mounted System
(ExacTrac System)
Isocenter calibration
phantom
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x-ray calibration phantom
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MV-kV calibration --- Elekta
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.
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. Adjustment of BB to treatment
isocenter
+1mm
qg
qg
u
v
-1mm
-180
qg
+180
Reconstruction
4. Measurement of BB location in kV
radiographic coordinates (u,v) vs. qg.
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Flex Maps: Synergy (XVI) Units
XVI1
26 cm
CCW
40 cm
CW
40 cm
CCW
50cm
CW
Long term stability for one unit (NKI)
50 cm
CCW
0.1
mean
+/- 2
0.05
U [cm]
FOV:
26 cm
Rot. Dir: CW
6. Use ‘Flex Map’ during routine
clinical imaging
5. Analysis of ‘Flex Map’ and
storage for future use
0
-0.05
XVI2
-0.1
-50
0
50
100
150
u
V [cm]
0.05
6 calibrations
over 15
month period
0
-0.05
-0.1
XVI5
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-100
0.1
XVI3
XVI4
v
-150
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-150
-100
-50
0
50
Gantry angle [o]
100
150
Weekly QA of MV/kV isocenter calibration
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All Flex Maps: Synergy (XVI) Units
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OBI1 Approach – “Residual”
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
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Accept if within specified tolerance.
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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
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Full kV/MV Calibration - Monthly
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Is o _ O D I = Q /A P h a n to m = L a s e rs / O D I
Compare Portal Image & DRR
E 2 (C B C T )
E 1 (E P ID ’s )
Is o _ k V
M V M e c h a n ic a l
Is o c e n te r
E3
M V N o m im a l
Is o c e n te r
z
Is o _ M V
M V R a d ia tio n
Is o c e n te r
y
x
Current* Action Level on E3: 2 mm (in any one direction)
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* Due to large observer variability in MV alignment
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2006 XVI Daily QA Results (E3 Error)
XVI1
XVI2
[mm]
M
XVI3
L/R
XVI4
S/I A/P
2007 OBI Daily QA Results (E3 Error)
XVI5
OBI1
[mm]
(-0.04, -0.72, 0.52)
of Daily QA Testing
L/R
OBI3
S/I
OBI4
A/P
M = (-0.08, -0.19, 0.27)
Ave(σ) (0.96, 0.82, 1.04)
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Months
OBI2
Ave(σ) = (0.51, 1.02, 0.71)
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CBCT:
Geometric Accuracy and Precision
IG Performance:
Connectivity,Orientation/Scale Checks
CBCT vs Orthogonal Portal Images
Phantom - Unambiguous Object
ic
etr
lum nce
Vo fere s
e
e
R
ag
Im
Elekta Synergy RP
CT
Simulation
Pl
an
ni
ng
CT
‟s
On
-lin
eI
ma
ge
s
OBI
Acquisition
XVI
Acquisition
D IC O M /R T
40 measurements over several months
Off-line Image
Review/Archive
M
CO
DI
T
/R
Treatment Planning System
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Sharpe et al. - Med Phys. 2006 Jan;33(1):136-44.
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IG Performance:
Connectivity,Orientation/Scale Checks
•
•
•
•
•
•
Anthropomorphic phantom
4 Orientations
Target bony anatomy
Arbitrary initial shifts
Plot residual error
5 XVI units
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Planning: Philips Pinnacle v7.4
. .
IG Performance:
Connectivity,Orientation/Scale Checks
Residual Absolute Error [cm]
Residual Error
Image Source: GE and Philips CT
0.18
0.16
0.14
0.12
L/R
S/I
A/P
0.10
0.08
0.06
0.04
0.02
0.00
1
All XVI‟s
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Baseline CBCT Imaging
X-ray source:
•Heat capacity
•Focal spot size
•Energy range
•Bow-tie filter
Bow-Tie Filter
Affects
•How often can you scan
•Resolution
•Contrast/dose – thick patients
•Image homogeneity
Flat-panel detector
•Quantum efficiency
•Size
•Resolution
•Speed
•Scatter grid
•Noise
•Size
•Resolution
•Angular sampling
•Image homogeneity / noise
Gantry
•Speed
•Accuracy (constancy)
•Speed
•Resolution
• Reduce Scatter
• Lower Skin Dose
• Reduce Saturation
30 mm
2 mm
Aluminum
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Application of a Bow-Tie Filter
No Bow-Tie
Effect of size (scan length) on image quality
Bow-Tie
2 cm
12 cm
20 cm
1 mm2 voxels, 1 mm slice
thickness, 32 mA, 40
ms, 120 kV, 1.5 cGy
Central dose 3 cGy, skin 4 cGy
Central dose 3 cGy, skin 3 cGy
2 minutes scan time
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Which dose to use?
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
0.25 cGy
0.5 cGy
• How much do you need?
– This depends on the task
2 cGy
1 cGy
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1 mm2 voxels, 1 mm slice thickness, 120 kV
Scatter grid
0.3 cGy
3.0 cGy
Dose
Projections
• Scatter grid attenuates
– + Scatter
– - Primary beam
0.1 cGy
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
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• Software correction may be equally effective
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Scatter correction algorithms
Reconstruction settings
•
•
•
•
•
Without correction
Slice thickness
Pixel size
Pre-filtration
Interpolation
Reconstruction filtration
With correction
Boellaard et al. Two-dimensional exit dosimetry using a liquidfilled electronic portal imaging device and a convolution model
Radiother. Oncol. 44 149-157, 1997
Elekta: scatter uniform and proportional to average image
intensity where there is patient in the beam
Varian TrueBeam: iterative kernel based scatter estimation
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Slice Thickness: 1 mm2 voxels, 20 mA, 20 ms, 120 kV, 1 cGy
1 mm slice thickness
3 mm slice thickness
1 mm
slice
thickness
5 mm slice thickness
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5 mm
slice
thickness,
averaged
in all
directions
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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
Elekta setting: smoothed
Un-smoothed
1 mm2 voxels, 1 mm slice thickness, 32 mA, 40 ms, 120 kV, bowtie, 3 cGy
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mm2
voxels, 0.5 mm slice thickness
0.5 mm2 voxels, 2.5 mm slice thickness
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Bench top CBCT System
Patient Dose Estimation: kV-CBCT
Dose depends on
•
•
•
•
•
Beam Quality: HVL (kVp, filtration)
Tube output: Reference (mR/ mAs)
Scanning Geometry: SAD, FOV, No. of projections
Technique settings: mAs
Patient Size (Body , Head…)
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AAPM’10
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CBCT: Radial Dose
Depth
Phantom: 30 cm dia.
Imaging Technique:
120 kVp
100 mA
20 ms
2.4
2.2
2.0
1.8
Dose (cGy)
Imaging Technique:
100 kVp
100 mA
20 ms
330 Projection
660 mAs
1.6
1.4
FOV:
FOV:
FOV:
FOV:
1.2
1.0
5 cm x 26cm
10 cm x 26cm
15 cm x 26cm
26 cm x 26cm
Depth
0.8
330 Projection
660 mAs
2.4
2.0
2
4
6
5 cm x 26cm
10 cm x 26cm
15 cm x 26cm
26 cm x 26cm
1.8
1.6
1.4
1.2
1.0
0.6
0
FOV:
FOV:
FOV:
FOV:
2.2
Dose (cGy)
Phantom: 16 cm dia.
CBCT: Radial Dose
0.8
8
Depth (cm)
0.6
0
2
4
6
8
10
12
14
Depth (cm)
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CBCT Imaging Dose: Offset Geometry (FOV 40 cm)
Clinical Imaging Dose Measurements
Dose vs. Field Size
Experimental Setup
2
Detectors
Detectors
Kim et al,
Total Dose (cGy)
A simple and
clinical feasible
method to
estimated the
CBCT imaging
dose
Nuclear Enterprises Free-Air
Chamber (0.6 cc)
32 cm “Body” Phantom
330 projections at 2 mAs / proj
Radiat Prot Dosi. 2008
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1.5
D2cm
1
Dcenter
0.5
0
0
10
20
30
Field Size (z) (cm)
Islam et al., Med. Phys. 2006
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Deciding the Necessary Image Quality for the Application
Variation of image quality with lens dose (cGy)
Low Dose (1.5 mGy) Pediatric Imaging
for Routine On-line IGRT
mAs/ Projection
2
1.0
2.0
0.5
1.0
4.0
16x
Reduction
1
2.0
0.5
0.25
80
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0.5
160
320
Number of Projections
1.0
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IGRT is Clinical Quality Assurance
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)
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• 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
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MV vs kV Fallacy
Off-Line In-Room Image-Guidance
• Daily orthogonal openfield 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
Patient planning information/
Patient information system
H&N
H&N
Lung
Lung
Patient setup
Pelvic
On-board images
Treatment
nth treatment
Statistical
Analysis (m,)
Y
Correction?
Reference images
N
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Clinical IGRT Strategies:
Margin --- from population to individual margin
On-Line In-room Image-Guidance
•
Patient planning information/
Patient information system
Patient setup
In-room imaging I
Reference images
On-board images
Correction?
Y
In-room imaging III
In-room imaging II
Feedback
ACMP 2011_jww
In-room imaging
Correct position
N
Key technologies for
quantifying treatment
uncertainties:
• Organ motion:
Computed
Tomography
• Daily setup:
Electronic Portal
Imaging
SI
Lat
Treatment
Conventional RT
Off-line Adaptive RT
On-line correction
Data: 1
Generic Margin
~ 2.5S + 0.7
Data: n < N
Corrects for
systematic error
Data: daily
Corrects for all
setup/motion errors
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Workflow Using Snap Verification
Image-Guidance with ExacTrac
Initial 6D setup
Snap
verification
for field 3
Snap
verification
for field 2
Snap
verification
for field 4
6D Robotics
Frameless
Radiosurgery
....
Adaptive Gating
Treat field 1
ExacTrac IGRT
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Use Case: Intra-Fraction Imaging
Treat field 2
Treat field 4
Treat field 3
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Image-Guidance with CT-on-Rails
Planning and R&V System
Room
Reference
CT dataset
Treatment Planning
R&V
System
Intranet
Image
Storage
Reference CT
Control Room
Imaging console
LINAC console
Gating
Signal
Alignment
Protocol
Correction?
Treatment
Room
Example of dual x-ray imaging
Couch
Shifts
LINAC
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Patient
couch
In-room
kV CT/CBCT
Images
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5/2/2011
Use Case – SBRT Pancreatic Cancer
•
•
•
•
•
•
ABC-kV AP setup
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
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ABC-kV lateral setup
kV intra-fx monitor at one beam angle
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Au markers validation:
MV vs. kV shift difference
Use Case: 3-D Free-Breath ITV with CBCT
vs
MV with Markers
CBCT with Markers
• Independent Alignment Methods
• 16 patients (~250 fx)
• Duration: 6 months
CBCT
images
after
correction
CBCTPost-treatment
images
prior
toCBCT
correction
Planning
CT with
target
contours
• Unambiguous Surrogate (3 Au markers)
Wang et al Ref J 2007
ACMP 2011_jww
ACMPMoseley
2011_jww
et al. Int. J. Rad. Onc. Biol. Phys., 63, 2007
Clinical “end-to-end” assessment of IGRT
Summary
Background
• The XVI system is linked to the Remote
Automatic Table Movement (RATM).
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.
• 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.
Sarcoma
9%
Lymphoma
3%
Upper GI
21%
Head and Neck
26%
Methodology
Lung
41%
• Collection Period Oct 19th „06 – Nov 17th „06
• Patients with repeat (verification) scans were
measured and matched using an Automatic
Algorithm
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
• 34 patients with 135 scans
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W Li et al. J Appl Clin Med Phys. 2009 Oct 7;10(4):3056
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5/2/2011
Summary
Future considerations for in-room x-ray IGRT
• 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.
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• 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
Contrast Enhanced CBCT – OBI 1.4
with no breathing motion
CBCT system
US system
Courtesy of Michael
Lovelock and Josh
Yamada MD; MSKCC
1a
(a)_
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(b)_
(c)_
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5/2/2011
Varian - Elekta
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
Parameter
Varian Truebeam
Energy range
40-140 kV
Elekta
XVI4.5
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
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