qa for the tomotherapy hi -art ™ · 2008-12-03 · tomotherapy patient target fan beam,...

Robert J. Staton, PhDMedical Physicist

QA for the TomoTherapy HiQA for the TomoTherapy HiQA for the TomoTherapy Hi---ArtArtArt™™™

Acknowledgements

Katja Langen, PhDSanford Meeks, PhD

MDACCO has received grant funding fromTomoTherapy, Inc.

Disclosures

The TomoTherapy units at MD Anderson Orlando

Tomo1 (SN 02) Tomo2 (SN 50)

Topics

• Review of the TomoTherapy system

• Commissioning and Twinning

• QA Program

• Routine

• After Component Replacement

• Patient DQA

• TQA

TomoTherapy

• Helical delivery of IMRT

• Same hardware is used for MVCT

• IGRT for every patient

Binary MLC(64 leaves – 6.25mm )

85 cm Gantry Aperture

40 cm CT FOV

85cm

Approximately 50cm

6 MV Accelerator

Primary Collimator

TomoTherapy

TomoTherapy

Patient

Target

Fan beam,

continuouslyrotates

OAR

TomoTherapy

each beamlet can be on/off for apercentage of each projection

Divides beam into 64 beamlets

TomoTherapy

Patient

Target

Fan beam,

continuouslyrotates

OAR

TomoTherapy

Fan beam,

continuouslyrotates

TomoTherapy

Fan beam,

continuouslyrotates

TomoTherapy

Fan beam,

continuouslyrotates

Fan Beam

400 mmlateral

10, 25, or 50 mm

longitudinal

lateral

longitudinal

Helical Tomotherapy

from: W. Kalender, Computed Tomography: Fundamentals,System Technology, Image Quality, Applications

Delivery

- 51 projections perrotation: 360º/51=7º

-Temporal modulationleaf opening timeduring projection

-Typical gantry rotation:15-30 seconds

-Typical treatment time:Prostate: 5 MinH&N: 7 Min

Delivery Instructions (Sinograms)

1 gantry rotation

Sinogram Sinogram

Sinogram

Binary MLC(all leafs open during MVCT)

85 cm Gantry Aperture

40 cm CT FOV

85cm

Approximately 50cm

6 MV Accelerator (tuned to 3.5 MV for MVCT)

Primary Collimator( 5 mm Slice Width)

Megavoltage CT images

IGRT using megavoltage CT images

Prostate Head + Neck

Commissioning• Done in conjunction with TomoTherapy physicist

• Machines are assembled and tested in thefactory and then partially disassembled forshipment

• Verify that the beam properties matches themachine data taken in the factory and the goldstandard

• TomoTherapy TPS uses gold standard data forall dose calculations

Commissioning Tests

• Hardware Alignment

• Source position

• Jaws

• MLC

• Lasers

• Beam

• Output Stability

• Beam Profiles - Transverse, Beam Width, PDD

• Static Output Calibration

• MVCT image quality

• IMRT phantom tests

Water Tank

Standard Imaging – 2D Scanning Tank

Scanning Data

0

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20 25

Do

se(N

orm

aliz

ed)

Distance (cm)

PDD 25 mm Field Width

Calculated

Measured

Install measured

Scanning Data

0

10

20

30

40

50

60

70

80

90

100

-300 -200 -100 0 100 200 300

Dos

e(N

orm

aliz

ed)

Distance (mm)

Cone 25 mm Field Width15mm Calculated

50mm Calculated

100mm Calculated

150mm Calculated

200mm Calculated

15mm Install Measured





Scanning Data

0

10

20

30

40

50

60

70

80

90

100

-25 -20 -15 -10 -5 0 5 10 15 20 25

Do

se(N

orm

aliz

ed)

Distance (mm)

Penumbra 25 mm Field Width 15mm Calculated

50mm Calculated

100mm Calculated

150mm Calculated

200mm Calculated






Commissioning - IMRT Tests

• On-axis and off-axis target for each beam

0.0

0.5

1.0

1.5

2.0

-20 -15 -10 -5 0 5 10 15 20

Do

se(G

y)

Distance (cm)

Calculated & Delivered Dose: 25mm Beam, On-Axis Tumor

Calculated

Measured

0.0

0.5

1.0

1.5

2.0

-20 -15 -10 -5 0 5 10 15 20

Do

se(G

y)

Distance (cm)

Calculated & Delivered Dose: 25mm Beam, Off-Axis Tumor

Calculated

Measured

Twinning

• For multiple machines, you can matchthe beam characteristics

• Recommissioning

• Facilitates the transfer of patients fromone machine to the other in case of downtime

After Commissioning

• End to End phantom tests

• H&N phantom

• Pelvis phantom

• Cheese phantom

• Film & Ion Chamber

• DQAs for phantom plans and test cases

• Independent calibration check - RPC TLDs

• Setup your QA program

• Daily QA

• Reference data for monthly and part replacement QA

• TMR/PDD in solid water

• TomoDose Profiles

QA Program

Routine:

Daily, Patient DQA, Monthly, Annual

After Component Replacement:

Magnetron, MLC, Target

Daily QA Output measurements:

• Static procedure, gantry at 0°, 5x40 cm field

• Readings taken at a depth of 5 cm and 10 cm

Daily Output Constancy

Daily Output Constancy

Hi*Art II, S/N 002

750

760

770

780

790

800

810

820

830

840

850

16-

Ma

r-03

6-Ju

n-03

27-

Au

g-03

17-

No

v-0

3

6-F

eb-

04

28-

Ap

r-04

19-J

ul-0

4

9-O

ct-0

4

30-

De

c-0

4

21-

Ma

r-05

11-

Jun-

05

1-S

ep-

05

22-

No

v-0

5

11-

Fe

b-06

4-M

ay-0

6

25-J

ul-0

6

15-O

ct-0

6

4-Ja

n-07

27-

Ma

r-07

17-

Jun-

07

7-S

ep-

07

28-

No

v-0

7

17-

Fe

b-08

Date

Out

put(

cGy)

(60

sec

Re

adin

gs)

+5%

-5%

+3%+2%

-3%-2%

Daily Output Summary

- Typically within 2 % of nominal output- If outside 3 %, adjust PFN (output) at end of day- Observed long term drifts

- About 2 weeks after magnetron replacement- End of target life

- Very temperature sensitive-if machine is not at operating temp. (38-40 ºC)output measurement can be unreliable

Daily Energy Constancy

+3 %+2 %

-3 %-2 %

HI*ART II S/N 002, ENERGY CHECK

0.4000

0.4050

0.4100

0.4150

0.4200

0.4250

0.4300

0.4350

10-D

ec-0

2

28-J

un-0

3

14-J

an-0

4

1-Au

g-04

17-F

eb-0

5

5-Se

p-05

24-M

ar-0

6

10-O

ct-0

6

28-A

pr-0

7

14-N

ov-0

7

1J

08

DATE

DEPT

HDO

SEAT

15cm

Daily IMRT Procedure

1) Scan 2 ) Register-compare toknown offsets

3) Align-test couch andlaser movements

4) Treat- two point dosemeasurements

Patient Plan DQA

- Deliver plan into phantom- Measure dose point with Ion chamber and dose

distribution with EDR film

DQA Setup

Ion chamber highdose, low gradientregion

DQA Setup

Calculate dose distribution in the phantom

DQA – Point Dose Measurement

TomoTherapy Point Dose Verification

Temperature 24.0 0C

Pressure 759.0 mm Hg

CTP 1.008

Electrometer Inovision 35040

Chamber Exradin A1SL, SN 30562

Phantom Solid H20 ("Cheese" Phantom)

System Calibration Factor (C21) 0.6660 [Gy/nC]

Ion Chamber Position In Phantom 1 BELOW Film Plane

Electrometer Reading for Phantom Irra 2.081 [nC]

Doseplan 1.381 [Gy]

Dosemeas 1.397 [Gy]

Ratio (Dmeas/Dplan) 1.012 Pass

1.1780 % Difference

DQA Film Analysis

Film

DQA film analysis

Expected isodose lines vs measurement

DQA Film Analysis

Film and dose profiles

DQA – Point Dose Measurement

5%3%

06-07 DQA Results

-10

-8

-6

-4

-2

0

2

4

6

8

10

12/14/2005

3/24/2006

7/2/2006

10/10/2006

1/18/2007

4/28/2007

8/6/2007

11/14/2007

Date

%D

iffer

ence

DQA with Array devices

Available array devices

Sun Nuclear – MapCHECK

IBA Dosimetry – Matrixx

PTW – 2D-ARRAY seven29

DQA with Array devices

Advantages:

Time savings

No film processing issues

Real time comparison

Disadvantages:

Resolution

Tomo DQA with MapCHECK

- Initial tests have shown good results forTomoTherapy DQA

-Gamma test results- Absolute dose (3%, 3mm)- HN: 98.5% passing- Prostate: 99.6% passing


Head and Neck


Prostate


Import into TomoTherapy

Monthly QA

-Output measurement with farmer chamber

-Laser alignments, x-z localization procedure

- Cone profile, lateral profile(TomoDose - diode array)

- Beam profile, longitudinal profile

- MVCT dose and HU

-Table position accuracy (ruler vs. readout)

Monthly QA





- MVCT dose and HU


Fan Beam

400 mmlateral

10, 25, or 50 mm

longitudinal

lateral

longitudinal

Check profile monthly

TomoDOSE

TomoDOSE lateral beam profile

0

0.2

0.4

0.6

0.8

1

1.2

-30 -20 -10 0 10 20 30

Off axis distance (mm)

Rel

ativ

eRea

din

g

Accuracy of TomoDOSE

Accuracy of TomoDOSE Monthly QA: Cone Profile

Monthly QA: Cone ProfileMonthly QA





- MVCT dose and HU


Longitudinal Profile

- Static Gantry at 0°- Continuous tablemovement

- Measure current

FWHM

Monthly QA





- MVCT dose and HU


Monthly MVCT QA

Test Consistency

HUNoiseUniformitySpatial resolutionDose

- takes 1 MVCT scan

1.56

1.824

0.48

0.33

Weekly QA (by TomoTherapy Service)

- Output- Cone beam profile

- Check error Log files- Check TCS- Check Data Server- Check various mechanical parameters

Weekly QA (by TomoTherapy Service)

- Output- Cone beam profile

- Check error Log files- Check TCS- Check Data Server- Check various mechanical parameters

Rotational Variation

Rotational Variation (by TomoTherapy Service)

Binary MLC

40 cm CT FOV

85cm

Approximately 50cm

6 MV Accelerator

Primary Collimator

- Treatment beam- All MLC leafs open- Rotate gantry- Collect detector data

- Compare detector datato Gold Standard

Rotational Variation Annual QA

-Beam data (PDD, long. and lateral profiles)

-Mechanical alignment tests (Jaw, MLC alignment)

�Follow TomoTherapy’s recommendedtest procedures

Annual QA, Beam Data

-Collect beam data for all (three) commissionedbeam widths (1.0, 2.5, 5.0 cm)

-Cheese Phantom based end-to-end tests

- RPC TLD

Phantom end-to-end test

1 cm 2.5 cm 5 cm

CentralTarget

+ 0.5 % + 2.8 % + 2.1 %

PeripheralTarget

+ 1.3 % + 1.0 % + 0.8 %

RPC TLD Measurements (Static Field)

20 s beam-on timewith 5x40 field gives~270 cGy to TLDs

Annual QA Alignment Tests

-Source should be aligned with center of jaw

Measure output at different jaw positionsMax output indicates jaw center


-Test Y-divergence and jaw twistFilm below iso, irradiate from 0º and 180º

Iso

Film

Aligned Jaw

Twisted Jaw

Divergence centeroff from rotation plane

Annual QA: Y-Divergence/Jaw Twist


-Source should be aligned with MLC

Run odd leaf only and even leaf only profileCompare to all leaf open profile -> T-G profileLook for symmetry in TG-Profile

Time Requirement

- Daily: Including warm up time: 1 hour

- DQA: 20-30 minutes per case

- Monthly: 2-3 hours

- Annual: 1-2 days

QA Following Major Component Replacement

MagnetronTypically every 3-4 months

Tomo service engineer-Adjusts beam profile and output using arotational variation procedure

Physicist: (2 h)-Check output and energy-Check beam profile using TomoDose array-Run 1-2 DQA procedures (IC+Film)


MLCTypically lasts about 18 Months

Tomo service engineer-Checks alignment with T+G test-Measures leaf latency

� update leaf latency file for future plans

Physicist: (3-4 h)-Check multiple current patient DQAs. 6-8 DQA


TargetTypically lasts 8-10 Months

Tomo service engineer-Checks Linac alignment-Adjusts beam profile and output using arotational variation procedure

Physicist: (1-2 days)- Beam profiles (TomoDose)� Do annual QA

Target Wear Warning Signs

Beam profile change:• Service engineers checks beam profiles weekly• Physics QA includes monthly TomoDOSE test

Target Wear Warning Signs Variations in lateral beam profile

TomoDOSE On-board detector

Energy Variation

+3 %+2 %

-3 %-2 %

HI*ART II S/N 002, ENERGY CHECK

0.4000

0.4050

0.4100

0.4150

0.4200

0.4250

0.4300

0.4350

10-D

ec-0

2

28-J

un-0

3

14-J

an-0

4

1-Au

g-04

17-F

eb-0

5

5-Se

p-05

24-M

ar-0

6

10-O

ct-0

6

28-A

pr-0

7

14-N

ov-0

7

1J

08

DATE

DEPT

HDO

SEAT

15cm

Target changes

Component replacement

Target :

• Can typically be predicted

• Scheduled over weekend

Magnetron :

• Fails suddenly

• 1 day (or one night job)

TomoTherapy TQA

• TQA software being released by TomoTherapy

• Uses detector data to measure beam properties anddelivery systems

• Output

• Beam Profile

• Energy

• Lasers

• Couch synchrony

• MLC

• Allows access to detector data for QA for developmentof personalized QA tests

Conclusion

Routine Machine QA:

• Comparable to other machines in terms of time

Major component replacement:

• More frequent than ‘regular’ Linac

• Some replacement can be predicted

• TQA may help with prediction of these failures

Thank You

qa for the tomotherapy hi -art ™ · 2008-12-03 · tomotherapy patient target fan beam,...

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