QA For IGRT

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


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


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


Radiographic Mode


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


Sample images

Images courtesy of Karolinska Institute


Kilovoltage Radiographs


Cone-Beam CT


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


Clinical Results Hirslanden Klinik, Aarau

CT

CBCT


CBCT

Clinical Results Emory

CBCT CT Simulator


Intrafraction motion


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


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


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


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


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

10


IGRT QA Safety

Daily checks kV source door interlock

Warning lights and audio warning for kV beam

Motion enable from OBI control console


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


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



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


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



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

13


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





Lat DRR Lat KV Image

Using the plan created from Eclipse, AP MV and Lat KV images were acquired (shown only Lat image)


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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





Long: __ mm OK 1.5 mm Long: __ mm OK 1.5 mm

Lat: __ mm OK 1.5 mm Vert: __ mm OK 1.5 mm


15


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


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

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IGRT QA Monthly Checks

Safety

OBI laser crosshair

Arms isocentric calibration

Arm run out

Blades calibration

Couch motion Linear

Rotation


IGRT QA Safety

Emergency off (part of Clinac QA)

Backup motion controller

17


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


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

18


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


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


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


IGRT QA Monthly Checks

Isocenter alignment of MV and kV beam

MV Image Quality

kV Image quality

Shift calculation

Measurement tools

20


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


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


21


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


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


22


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


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


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



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


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


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


25


Measurement tools

Measurement of

Distance

Area

Angle


IGRT QA Annual Checks

Annual checks kV beam output parameters

kV, mA, exposure time

HVL

Automatic Brightness Control (ABC) for fluoroscopy

26


IGRT QA CBCT Tests

Daily checks Geometry

HU calibration spot check

Annually (Monthly) Uniformity

Contrast

Resolution

HU calibration


CBCT Daily Check

Position CATPHAN on the table

Acquire CBCT

Verify geometry

Verify HU

27


CBCT Annual test

Position Norm Phantom on the table

Acquire CBCT

Measure profile and verify uniformity of HU


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


28


Contrast

Performance 0.5 %


Resolution

Performance 10 lp/cm

29


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



HU Calibration

1. Air =-1000

2. LDPE = -100

3. Acrylic = 120

4. Teflon = 990

30


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



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

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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


QA Tools delivered with OBI and CBCT

Cone Beam CT NORM calibration phantoms

CATPHAN

32


Norm calibration

Norm Phantom To correct for scatter

2 Norm phantoms Head

Body

CATPHAN Geometry

Resolution

HU

Contrast


Examples of QA Protocols Courtesy of Sua Yoo, PhD, Duke University

33


Daily OBIDaily OBI Weekly OBIWeekly OBI


Monthly OBIMonthly OBI

(continues)

34


Monthly CBCTMonthly CBCT

(continues)


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


Automated IGRT QA Works in Progress

Courtesy Lei Xing, Stanford


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

Documents

QA For IGRT