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1VARIAN Medical Systems
Quality Assurance for IGRT
Roman Wicha, PhDVarian Medical Systems
Stanford IGRT Course 2008
VARIAN Medical Systems
IGRT QA
Agenda VMS IGRT Solution
IGRT QA Tests
QA Tools
Examples of QA Protocols
Summary
2VARIAN Medical Systems
VMS IGRT Solution -On-Board ImagerTM (OBI)
X-ray Source- Varian G242
aSi Imaging Panel- Varian PaxScan 4030CB
Robotic Arms- 3 pivot points:
Shoulder, elbow and wrist
- Completely retractable
- Position feedback control
Software- Custom software for image
acquisition and registration
VARIAN Medical Systems
VMS IGRT Solution
On Board Imager Radiographic mode
Fluoroscopic mode
Interaction with Respiratory Gating (RPM) System available
Cone Beam CT (CBCT) Acuity
Hi-Energy Linear Accelerator
3VARIAN Medical Systems
Radiographic Mode
VARIAN Medical Systems
1. Setup patient
2. Extend arms
3. Exit treatment room
4. Remotely acquire AP and lateral kV images
5. Compare current images to reference images (DRRs)
Automated
Manual
6. Calculate couch motion required to correct setup
7. Move couch remotely
8. Reacquire and reanalyze to confirm setup correction
9. Retract arms remotely
10. Treat
Radiographic Mode: Anatomy
4VARIAN Medical Systems
Sample images
Images courtesy of Karolinska Institute
VARIAN Medical Systems
Kilovoltage Radiographs
5VARIAN Medical Systems
Cone-Beam CT
VARIAN Medical Systems
1. Setup patient
2. Extend arms
3. Exit treatment room
4. Acquire CBCT Dataset
5. Compare current images to reference CT images
Manual
Automated
6. Calculate couch motion required to correct setup
7. Move couch remotely
8. Reacquire and reanalyze to confirm setup correction?
9. Retract arms remotely
10. Treat
CBCT Mode
6VARIAN Medical Systems
Clinical Results Hirslanden Klinik, Aarau
CT
CBCT
VARIAN Medical Systems
CBCT
Clinical Results Emory
CBCT CT Simulator
7VARIAN Medical Systems
Intrafraction motion
VARIAN Medical Systems
Pretreatment Fluoroscopic Verification of Gating
Setup patient
Extend arms
Rotate gantry to first field
Exit treatment room
Remotely acquire fluoro
MLC aperture turns green/red, indicating when the gate is open/closed
Verify target remains within aperture
Repeat for other fields
Retract arms remotely
Treat
8VARIAN Medical Systems
IGRT QA
Number of IGRT installations is increasing
There are limited guidelines for QA available as of now Yoo et all., A quality assurance program for the on-
board imager, Medical Physics, Vol. 33, No. 11, November 2006
IGRT QA should contain All the tests done for 3D CRT and IMRT
Additional test related to image guidance
VARIAN Medical Systems
IGRT QA
Primarily a machine QA
There are no patient specific tests for IGRT (on top of the ones performed for IMRT)
Parameters to be tested Safety
Mechanical and optical
X-Ray beam
Imaging
Functionality
9VARIAN Medical Systems
IGRT QA Daily Checks
Anti-collision system
Warning lights and audio warning for kV beam, interlocks
Motion enable from OBI control console and hand pendants
kV source / kV detector / MV detector positioning accuracy
VARIAN Medical Systems
Daily checks Anti-collison
Detector Front
Side
Arm
Source Front
Side
Back
Arm
Detector Front
Side
MV detector arm kV source arm kV detector arm
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IGRT QA Safety
Daily checks kV source door interlock
Warning lights and audio warning for kV beam
Motion enable from OBI control console
VARIAN Medical Systems
Motion Enable
Detector and arm motion is only possible when motion enable bars on the hand pendant or motion enable button on the OBI console are pressed
11
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Position calibration Daily Option 1
Vertical axis calibration Position arms to the predefined position
(e.g. kVS 100cm, kVD 50 cm, MVD 50 cm)
Measure distance from detector cover / kV source plate to the isocenter
VARIAN Medical Systems
Position calibration Daily Option 2
Longitudinal and lateral axis calibration Position kV Blade Calibration Plate on the table
Move table to the isocenter
Align kV Blade Calibration Plate with Clinac crosshair
Acquire an image
Compare position of digital graticule with the center cross of the plate
12
VARIAN Medical Systems
Position Calibration Daily - Option 2
Tolerance displacement < 2 mm
Procedure Set Gantry 90o, measure the Lat displacement of
KVD using ceiling laser and measure the Vertical displacement using cross-hair
Set Gantry 270o, measure the Lat displacement of KVS using ceiling laser and measure the Vertical displacement using cross-hair
VARIAN Medical Systems
Position calibration Daily Option 3
The Cube Isocenter Phantom was used for this daily QA procedure Two sets of 1-mm lead shots (bbs) were used to define 2 separate
spatial locations (points)
In each set, one bb is on the anterior side (AP bb) and the other (Lat bb) is on the lateral side of the phantom
The first set defines the isocenter and the second set defines a point 1.5 cm anterior, inferior, and lateral from the isocenter
Adapted from Rabih Hammoud
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The OBI daily QA procedure starts with setting up the Cube phantom center (central bb set) at the mechanical isocenter of the linac by using the cross hairs projections anteriroly and laterally
Position calibration Daily Option 3
Adapted from Rabih Hammoud
VARIAN Medical Systems
Position calibration Daily Option 3
Lat DRR Lat KV Image
Using the plan created from Eclipse, AP MV and Lat KV images were acquired (shown only Lat image)
Adapted from Rabih Hammoud
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Lat DRR AP DRRKV Lat Image MV AP Image
The alignment of the central bbs with the digital graticule (representing the imager isocenter) will be checked from both AP and Lat images
Position calibration Daily Option 3
Adapted from Rabih Hammoud
VARIAN Medical Systems
Position calibration Daily Option 3
Long: __ mm OK 1.5 mm Long: __ mm OK 1.5 mm
Lat: __ mm OK 1.5 mm Vert: __ mm OK 1.5 mm
Adapted from Rabih Hammoud
15
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Results
MV Isocenter Check
00.20.40.60.8
11.21.41.6
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31Daily measurement (days)
Dai
ly m
ism
atch
di
stan
ce (m
m)
S/IR/L
Courtesy of Rabih Hammoud, presented at AAPM
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Results
KV Isocenter Check
00.20.40.60.8
11.21.4
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31Daily Measurement (days)
Dai
ly m
ism
atch
dist
ance
(mm
)
S/IA/P
Courtesy of Rabih Hammoud, presented at AAPM
16
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IGRT QA Monthly Checks
Safety
OBI laser crosshair
Arms isocentric calibration
Arm run out
Blades calibration
Couch motion Linear
Rotation
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IGRT QA Safety
Emergency off (part of Clinac QA)
Backup motion controller
17
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OBI Laser Crosshair
Using Clinac lasers position Isocenter cube to the isocenter
With gantry at 0, position kV source arm to 100 cm
Switch on OBI laser and verify its projection on the cube
Repeat for gantry angles 90, 270
VARIAN Medical Systems
Arms Isocenter Calibration
Position kV arm to 0,0,0 and verify that the center of the detector is aligned with the isocenter of the machine
Repeat for MV arm
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VARIAN Medical Systems
Arm run out - I
Position arm to 0,0,20
Verify that the crosshair or OBI laser projection is aligned with the center of the detector
Move detector along the vertical axis and verify the run out throughout the whole range of the motion
VARIAN Medical Systems
Arm run out - II
Position kV Blade Calibration Plate on the table
Move table to the isocenter
Align kV Blade Calibration Plate with Clinac crosshair
Position arm to 3-4 different positions along the vertical axis (e.g. 20, 40, 50, 70)
Acquire image at each position
Compare position of digital graticule with the center cross on the Calibration Plate
19
VARIAN Medical Systems
Blades calibration
Done using fluoro mode
Blade calibration tool placed at isocenter
Set up blades to given size
Verify blades alignment with the calibration tool
VARIAN Medical Systems
IGRT QA Monthly Checks
Isocenter alignment of MV and kV beam
MV Image Quality
kV Image quality
Shift calculation
Measurement tools
20
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Isocenter Accuracy
Tolerance Coincidence of treatment isocenter and
imaging center < 1.5 mm
Preparation Phantom with a center marker
QA plan with a setup field (AP or Lat) and DRR
Courtesy of Dr. Sua Yoo, Duke University
VARIAN Medical Systems
Procedure Set the phantom center at the isocenter based on calibrated
lasers, crosshair, and SSD
Acquire a kV image in OBI
Measure the displacement of the center marker from the center of the graticule in OBI
Blade Calibration PlateCube phantom
Marker phantom
Isocenter Accuracy
Courtesy of Dr. Sua Yoo, Duke University
21
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Tolerance Accuracy isocenter over gantry rotation < 2 mm
Preparation Volume phantom with a center marker QA plan with setup fields of various gantry/source
angles 0o, 90o, 180o, and 270o
Isocenter over Gantry Rotation
Modified from Dr. Sua Yoo, Duke University
VARIAN Medical Systems
IsocenterIsocenter accuracyaccuracy(May 2005 (May 2005 Apr 2006)Apr 2006)
: Error in phantom setup Re-QAX: Laser misalignment Laser adjusted
: Error in KVD calibration KVD re-calibrated
IsocenterIsocenter over gantry rotationover gantry rotation (Dec, 05 (Dec, 05 July, 06)July, 06)
G270 S
I
S
I
S
I
S
I
L R P A R L A P
G0 G90 G180
-0.2
-0.1
0.0
0.1
0.2
1 2 3
Dis
plac
emen
t (cm
)
Mechanical accuracyMechanical accuracy(May 2005 (May 2005 Apr 2006)Apr 2006)
Ver Long Lat
KVS
KVDKVS
KVD KVSKVD
Courtesy of Dr. Sua Yoo, Duke University
22
VARIAN Medical Systems
MV Image Quality
Set up detector
Place phantom on top of the detector
Acquire and analyze image (use Quality setting in the sequence template) max R determines contrast
max C determines resolution
VARIAN Medical Systems
IGRT QA Imaging chain
Weekly checks Image quality with imaging phantom
Monthly checks High contrast resolution
Gray scale linearity
Low contrast sensitivity
Image geometry Distance
Angle
23
VARIAN Medical Systems
Low contrast resolution Tolerance: > 11 12 disksFluoro: 70 kVp, 32 mA, 6ms 11 13 disksRadio: 75 kVp, 25 mA, 6ms 13 15 disks Spatial resolution Tolerance: > 11th groupFluoro: 50-80kVp, 80mA, 32ms 9 11th groupRadio: 50-80kVp, 80mA, 120ms 10 12th group
Fluoroscopic Radiographic
Results Image Quality
Courtesy of Dr. Sua Yoo, Duke University
VARIAN Medical Systems
IGRT QA OBI Shift calculation
OBI Geometric Phantom Crosshair #1 reference
Crosshair #2 test
Crosshairs shifted by the known distance
4 markers inside phantom
Reference image for setup fields at reference crosshair
kV/kV, MV/kV and Marker Match for fields setup at test crosshair
Verify distance calculated by OBI algorithm
24
VARIAN Medical Systems
Tolerance Accuracy of 2D2D match and couch shift <
2 mm Preparation
Phantom1. Phantom with off-center markers at
known positions, or 2. phantom with a center marker placed
at known position. QA plan with orthogonal setup fields and
DRR
Phantom Setup at Iso
kV images (AP/Lat)
2D2D match
Apply couch shift
Remote shift couch
Match DRRs graticuleto off centered marker
Verify couch in room
Before match After match Courtesy of Dr. Sua Yoo, Duke University
Shift Calculation 2D / 2D
VARIAN Medical Systems
2D2D match and couch shift2D2D match and couch shift(May 2005 (May 2005 Apr 2006)Apr 2006)
-1
0
1
2
Dis
agre
emen
t (m
m)
-2
-1
0
11 2 3
Diff
eren
ce (m
m)
2D2D match accuracy Couch shift accuracy
Ver: Ant +/Post ; Long: Inf +/Sup ; Lat: Rt +/Lt
Ver Long
LatVer Long Lat
Results
Courtesy of Dr. Sua Yoo, Duke University
25
VARIAN Medical Systems
Measurement tools
Measurement of
Distance
Area
Angle
VARIAN Medical Systems
IGRT QA Annual Checks
Annual checks kV beam output parameters
kV, mA, exposure time
HVL
Automatic Brightness Control (ABC) for fluoroscopy
26
VARIAN Medical Systems
IGRT QA CBCT Tests
Daily checks Geometry
HU calibration spot check
Annually (Monthly) Uniformity
Contrast
Resolution
HU calibration
VARIAN Medical Systems
CBCT Daily Check
Position CATPHAN on the table
Acquire CBCT
Verify geometry
Verify HU
27
VARIAN Medical Systems
CBCT Annual test
Position Norm Phantom on the table
Acquire CBCT
Measure profile and verify uniformity of HU
VARIAN Medical Systems
Half fanFull fanROI
Center
Left
Bottom
Right
Top
15.6 11.318.0 9.0
- 15.9 9.6- 8.5 7.8
- 13.4 10.1- 7.3 8.4
- 14.6 11.6- 3.4 8.9
- 14.6 10.4- 4.8 8.7
Full-fan Half-fan
Results HU Uniformity
Courtesy of Dr. Sua Yoo, Duke University
28
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Contrast
Performance 0.5 %
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Resolution
Performance 10 lp/cm
29
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Half fanFull fanTolerance
Spatial linearity
Slice thickness
Spatial resolution
Low contrast resolution
49.8 50.0 49.8 50.2 0.5 mm
2.45 2.512.39 2.60 0.1 mm
Group 6Group 8Group 6
Disk 4Disk 5Disk 4
Full-fan Half-fan
Low
con
tras
tre
solu
tion
Spat
ial
reso
lutio
n
Results CBCT Image Quality
Courtesy of Dr. Sua Yoo, Duke University
VARIAN Medical Systems
HU Calibration
1. Air =-1000
2. LDPE = -100
3. Acrylic = 120
4. Teflon = 990
30
VARIAN Medical Systems
Air
PMP
LDPE
Poly-
Acrylic
Delin
Teflon
- 995.7 13.3- 998.3 2.4
- 206.5 12.7- 196.6 8.6
- 106.9 16.1- 101.2 8.8
- 48.5 10.5- 42.8 8.8
116.1 12.396.0 9.0
354.0 15.1363.1 10.7
1007.8 22.8989.0 10.5
Half fanFull fan Full-fan Half-fan
Results HU linearity
Courtesy of Dr. Sua Yoo, Duke University
VARIAN Medical Systems
QA Tools delivered with OBI and CBCT
On Board Imager Isocenter cube
Blade calibration plate
Leads TORR-18FG phantom
OBI geometric phantom on Exact Bar
RPM RPM Gating phantom
31
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On-Board Imager Phantoms
RPM-Gating phantom:gated radiographs
and pretreatment fluoroscopic verification of gating
Leeds TORR-18FG Phantom: kV image quality
OBI Geometric Phantom: overall accuracy
and precision of the system
kV Blade Calibration Plate: calibrate the kV blades
Isocenter Cube:alignment of the kV to the
MV beam
VARIAN Medical Systems
QA Tools delivered with OBI and CBCT
Cone Beam CT NORM calibration phantoms
CATPHAN
32
VARIAN Medical Systems
Norm calibration
Norm Phantom To correct for scatter
2 Norm phantoms Head
Body
CATPHAN Geometry
Resolution
HU
Contrast
VARIAN Medical Systems
Examples of QA Protocols Courtesy of Sua Yoo, PhD, Duke University
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Daily OBIDaily OBI Weekly OBIWeekly OBI
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Monthly OBIMonthly OBI
(continues)
34
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Monthly CBCTMonthly CBCT
(continues)
VARIAN Medical Systems
Automated IGRT QA Works in Progress
IGRT QA is straightforward, but may require some time to acquire and analyze data
It maybe possible to automate some of the QA steps Weihua Mao, Louis Lee, and Lei Xing -
Development of a QA phantom and automated analysis tool for geometric quality assurance of on-board MV and kV x-ray imaging systems, submitted to Med. Phys.
35
VARIAN Medical Systems
Automated IGRT QA Works in Progress
Courtesy Lei Xing, Stanford
VARIAN Medical Systems
Summary
OBI and CBCT are increasingly used in the clinical routine
Development of commissioning and QA procedures is needed to accomplish safe delivery of IGRT
QA should cover Safety
Mechanical and optical
Imaging
Functional tests