The Role of In-Room kV X-Ray
Imaging for Patient Setup and
Target Localization (TG104)
Fang-Fang Yin, PhD
Duke University Medical Center
ACMP, May 2009
Members of TG 104
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
Objectives
1. Understand the current existing kV x-ray systems used in
the radiation treatment room, including system
configurations, specifications, operation principles, and
functionality.
2. Understand the current clinical application methods
about how these systems could be used to improve
treatment accuracy and their limitations.
3. Understand issues related to effective implementation in
the routine clinical procedures.
4. Understand issues related to acceptance testing and
quality assurance.
Charges of TG 104
a) Review the current existing kV x-ray systems used in
the radiation treatment room, including system
configurations, specifications, operation principles,
and functionality
b) Discuss the current clinical application methods
about how these systems could be used to improve
treatment accuracy and their limitations.
c) Discuss issues related to effective implementation in
the routine clinical procedures
d) Discuss issues related to acceptance testing and
quality assurance
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
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
Why In-Room Image-Guidance?
Accurate but
not precise
IGRT
Precise but
not accurate
IMRT
Precise and
accurate
IGRT+IMRT
Yin et al Sem Rad Onc 2006
History of In-room kV Imaging
Early days 50th ~ 60th:
• A separate kV x-ray system and Cobalt-60 treatment 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 90 degrees from
each other on a circular ring (Netherlands Cancer Institute)
• A Cobalt-60 unit with an x-ray tube mounted to the collimator at a
well defined angle with a graticule for optical and radiographic
projections (Shorvon, Robson et al. 1966)
History of In-room kV Imaging
kV x-ray source
Ontario Cancer Institute's X-otron Cobalt-60 unit
History of In-room kV Imaging
Continuous efforts 80th ~ 90th:
• An off-set kV x-ray source to a 10 MV medical accelerator at MGH
(Biggs, Goitein et al. 1985)
• A cobalt-60 treatment beam and an offset gantry mounted kV beam
on the same screen/film system (Shiu, Hogstrom et al. 1987)
• An add-on kV source: RADII product by HRL Inc
• A test for a low-Z accelerator targets for generating kV or near-kV xrays for imaging (Galbraith 1989; Ostapiak, O'Brien et al. 1998)
• A design of a new x-ray target for producing both kV and MV beams
(Cho and Munro 2002)
History of In-room kV Imaging
Modern IGRT 90th ~
• A CT scanner with the medical accelerator in the treatment room
(Akanuma, Aoki et al. 1984; Uematsu, Fukui et al. 1996)
• A proposed concept to integrate a kVCT/Linac system for the inroom image guided process (Mackie, Holmes et al. 1993)
• The dual orthogonal kV imaging systems, the first version of the
CyberKnife system (Murphy and Cox 1996)
• A pair of wall-mounted x-ray tubes and a novel portable CCDbased imager (Schewe, Lam et al. 1998)
• 4 ceiling mounted fluoroscopic imagers and 4 opposing floor
mounted kV sources (Shirato, Shimizu et al. 2000)
• Ceiling/floor-mounted kV image guidance methods for
radiosurgery by BrainLab Inc. in 2001 (Yin, Ryu et al. 2002)
History of In-room kV Imaging
Modern IGRT 90th ~
• A dual-beam (kV/MV) imaging system mounted to gantry: 37
degrees apart kV and mV (Sephton and Hagekyriakou 1995)
• A dual-beam (kV/MV) imaging system mounted to gantry: 45 and
then 90 degrees from the MV source with CBCT (Jaffray, Chawla
et al. 1995, Jaffray, Drake et al. 1999).
– Synergy accelerator by Elekta
– On-Board Imager (OBI) by Varian in 2003
– Artiste solution proposed by Siemens in 2007
• A hybrid imaging system: Varian OBI/CBCT system + the
BrainLAB floor/ceiling mounted system in 2008
Rail-track Mounted System
Varian-GE ExaCT™ system
Curtsey of Lei Dong, Ph.D., MD Anderson Cancer Center, TX
Rail-Track Mounted System
From C Ma
Siemens Primatom system
Curtsey of Lisa Grimm, Ph.D., Morristown Memorial Hospital, NJ.
Ceiling/Floor-Mounted System
Novalis
system
SDD: 3.62 m
SID: 2.34 m
Pixel: 0.4 mm
Matrix: 512x512
Digital
Detector
kV x-ray
tube
F-F Yin Med Phy 2002
Ceiling/Floor-Mounted System
Cyberknife system
X-ray tube
X-ray tube
Detector
Recessed Detector
Detectors under the floor
Detectors above the floor
Curtsey of Accuray, Inc.
Gantry-Mounted System
Synergy system
Gantry-Mounted System
On-board Imager
(OBI) system
Hybrid Image-Guidance System
NovalisTx
System
Duke University
Medical Center
KV Detector
Video/IR Camera
OBI KV
Detector
OBI KV tube
MV Detector
Recessed ExactTract
KV tube
Commercially Available Systems for In-Room kV Imaging
X-ray Imaging in Proton Treatment
Courtesy of Loma Linda University
Courtesy of Heidleberg
University
In-Room kV Image-Guidance Strategy
• Off-line
–
–
–
–
–
2-D planar imaging for surrogate imaging
Real-time fluoroscopic imaging for motion
Tomographic imaging for volume
4-D tomographic imaging for motion
3-D images for dose calculation
• On-line
–
–
–
–
–
2-D planar imaging for surrogate imaging
Real-time fluoroscopic imaging for motion
Tomographic imaging for volume
4-D tomographic imaging for motion
3-D images for dose calculation
Off-Line In-Room Image-Guidance
Patient planning information/
Patient information system
Next treatment
Patient setup
In-room imaging
Treatment
On-board images
Correct position
Y
Correction?
N
Reference images
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
Correct position
N
Treatment
2-D/3-D In-room Image-Guidance
• On-line systems
• Ceiling/floor-mounted system
• Gantry-mounted system
• On-line techniques
•
•
•
•
Real time 2-D radiographic imaging
Real time 2-D fluoroscopic imaging
2-D to 3-D image fusion
Automatic patient/beam positioning
3-D/4-D In-room Image-Guidance
• On-line systems
• Rail-track-mounted system
• Gantry-mounted system
• On-line techniques
•
•
•
•
Real time 4-D radiographic imaging
Real time 2-D fluoroscopic imaging
3-D and/or 4-D image fusion
Automatic patient/beam positioning
Image-Guidance with ExacTrac
6D Robotics
Frameless
Radiosurgery
Adaptive Gating
ExacTrac IGRT
Workflow Using Snap Verification
Initial 6D setup
Snap
verification
for field 2
Snap
verification
for field 3
Snap
verification
for field 4
....
Treat field 1
Treat field 2
Treat field 3
Treat field 4
Use Case: Intra-Fraction Imaging
Example of dual x-ray imaging
Image-Guidance with CT-on-Rails
Planning and R&V System
Room
Reference
CT dataset
Treatment Planning
R&V System
Image
Storage
Reference CT
Control Room
Imaging console
LINAC console
Gating
Signal
Treatment
Room
Intranet
Alignment
Protocol
Correction?
Couch
Shifts
LINAC
Patient
couch
In-room
kV CT/CBCT
Images
Use Case: IGRT for Liver Tumor
CBCTs
2-D Images
On-Board Imaging
Use Case: IGRT for Brain with CBCT
Onboard verification
Plan
Use Case: 3-D Free-Breath ITV with CBCT
CBCT
images
after
correction
CBCT
images
prior
to
correction
Planning
CT with
target
contours
Post-treatment
CBCT
Wang et al Ref J 2007
Overall Localization Accuracy
kV OBI
vs
Laser
Pre-tx CBCT
vs
2D kV OBI
Post-tx OBI
vs
Pre-tx CBCT
Mean Absolute Displacement (cm)
AP
CC
ML
AP
CC
ML
AP
CC
ML
0.32
0.35
0.36
0.26
0.19
0.22
0.08
0.09
0.07
RMS (cm)
0.60
0.39
0.14
123 Treatments of 40 lesions in 33 patients
Yoo et al ASTRO 2007
Image-Guided Implementation
• Identification of a Suitable Imaging Technology
• Design, Implementation and Maintenance
– Image Performance and Objectives
– Image Acquisition
– Analysis Tools
•
•
•
•
On-line and Off-line Strategies
Margins, Accuracy, and Precision
Decision-Making and Intervention
Quality Assurance Program for Image-Guided
Processes
• Imaging Dose Considerations
• Manpower and Training
Image Analysis & Patient Position Tool
Daily Bladder
as image
Bladder in
planning CT as
contour overlay
In-room CT
Hardware
and
software
application
and
verification
Bony Structure is off
Variable rectal filling
observed
In-room CT
Prostate target is aligned with
the CT image
Reference CT
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
Acceptance Testing: Imaging System
• Room design and shielding consideration
• Verification of Imaging System Installation
• Safety and Mechanical Configurations
• Geometric Calibration
• Localization Accuracy
• Image Quality
Commissioning: Imaging System
• Experimentally determine imaging parameters
for optimal image quality and localization
accuracy for different anatomical sites
• Identify potential limitations of the imaging
system
• Setup and document operation procedures for
different localization purposes
Quality Assurance Programs
• Goals:
– To ensure that the imaging systems, including both
hardware and software, function safely and
reproducibly, and perform as accepted and
commissioned
• Contents:
– Parameters, phantoms and measurement method
– Frequency and criteria
– Who and documentation
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
QA for Gantry-Mounted System
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
θg
θg
u
v
-1mm
-180
θg
+180
Reconstruction
4. Measurement of BB location in kV
radiographic coordinates (u,v) vs. θg.
5. Analysis of ‘Flex Map’ and
storage for future use
6. Use ‘Flex Map’ during routine
clinical imaging
Image Quality QA for OBI
Measurement
setup
Image for QA analysis
CT number
check for CBCT
QA for OBI/CBCT
• Safety and functionality
– Door interlock, collision interlock, beam-on sound, beam-on lights,
Hand pendant control, and network-flow.
– All test items are verified during tube warm-up (< 5 min)
• Geometric accuracy
–
–
–
–
OBI isocenter accuracy
Accuracy of performance for 2D2D match and couch shift
Mechanical accuracy (arm positioning of KVS and KVD)
Isocenter accuracy over gantry rotation
• Image quality
– OBI (radiography): contrast resolution and spatial resolution
– CBCT (tomography): HU reproducibility, contrast resolution, spatial
resolution, HU uniformity, spatial linearity, and slice thickness.
Calibration for Ceiling/floor-Mounted
System (ExacTrac System)
Isocenter calibration
phantom
x-ray calibration phantom
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)
Crescent Artifact in CBCT Scans
An apparent shift of
the bow tie profile
from projection to
projection deriving
most likely from
minor mechanical
instabilities, such as
a tilt of the source or
a shift of the focal
spot
Dose/Exposure vs Imaging Modality
Murphy et al
Med Phys 2007
TG 76 Report
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
New Development
•
•
•
•
CBCT with a Mobile CT
Dual X-Ray Tubes with Dual Detectors
kV and MV Dual-Energy Imaging
Digital Tomosynthesis
CBCT with a Mobile C-Arm System
Challenge:
How to correlate
imaging coordinate
with treatment unit
coordinate
C-arm system
www.Siemens.com
In-Line kVision Image-Guidance
System
Proposed ARtISTE system by
Siemens
The kV x-ray axis is in
parallel and coincident to
the treatment beam but at
the opposite direction
Radiographic
Fluoroscopic imaging
kV CBCT
www.Siemens.com
Dual X-Ray Tubes with Dual Detectors
Integrated
radiotherapy
imaging system
(IRIS): design
considerations of
tumour tracking
with linac gantrymounted diagnostic
x-ray systems with
flat-panel detectors
Berbeco et al
Phys. Med. Biol. 2004
A New Hybrid Image-Guided
Radiotherapy System
KAMINO et al, IJROBP 2006
Digital Tomosynthesis (DTS)
Scan angle
Compare to 2-D radiograph:
Patient
- Reduce overlying structure
- 3D information
- more dose (20-40 degrees)
Compare to 3-D CT or CBCT:
- Fast acquisition (5 s ~ 60 s)
- Lower radiation exposure
- Less collision limitations
On-Board H & N DTS Imaging
DRR
Onboard
R-DTS
Onboard-DTS
R-CT
Onboard-CBCT
Wu et al IJROBP 2007
On-Board Liver DTS Imaging
10-degree
20-degree
40-degree
Fuller et al ASTRO 2007
On-Board Breast DTS Imaging
CBCT
DTS
Coronal
Sagittal
Oblique
Zhang et al AAPM 2007
On-Board 4D-DTS Imaging
30-degree
gantry
rotation
Maurer et al AAPM 2009
kV/MV Dual-Beam CBCT Images
kV+MV CBCT
Diag CT
Yin et al.
Med Phys 2005
Zheng et al 2007
MV-CBCT
kV-CBCT
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.
Summary
Implementation of an in-room kV imaging technology
requires rigorous characterization and validation of its
performance.
Quality assurance measures with phantoms are requisite.
Expertise must be developed and must be re-established
from time to time. One must also be cognizant that in actual
clinical practice, inherent uncertainties of the guidance
solution exist, as each technique has its own range of
uncertainties.
Summary
There is uncertainty in the strength of the surrogate
information as in the case of implanted fiducials; in the
integrity of the information with time as in the case of CT
guidance; and in the residual error related to the
implementation of the correction.
In-room kV guidance clearly offers great potential of
improving treatment accuracy. The promise of in-room kV
guidance can only be realized with a radiation community
that applied the technology with discipline.
Acknowledgements:
Some research works are partially
supported by grants from NIH, Varian
Medical Systems, and GE Health Care.
Thank you for your attention.
The basic QA requirements for in-room kV
imaging system should include all items
listed below except:
0%
9%
86%
0%
6%
1.
2.
3.
4.
5.
Geometric accuracy
Dosimetric accuracy
Output factor
Image quality
Imaging dose
The differences between on-line and
off-line corrections are
83%
2.
0%
3.
11%
4.
On-line correction takes image(s) for the current treatment session
and makes correction for the next treatment session
On-line correction takes image(s) for the current treatment session
and makes correction for the current treatment session
Off-line correction takes image for the current treatment session
and makes correction for the current treatment session
Off-line correction cannot correct systematic errors
0%
5.
Off-line correction can correct both systematic and random
6%
1.
The following statements are all
correct except
3%
1.
6%
2.
75%
6%
11%
3.
4.
5.
The ceiling/floor-mounted kV imaging systems are able to
perform fluoroscopic imaging
The gantry-mounted kV imaging systems are able to perform
2-D radiographic imaging and cone-beam CT
The ceiling/floor-mounted systems can be used to acquire
cone-beam CT
The gantry-mounted kV imaging systems can be used to
acquire digital tomosynthesis images
The rail-track-mounted systems can not be used to acquired
real-time 2-D images during the radiation delivery