Andrew Godley

Joint Ohio River Valley

Penn-Ohio

Chapter meeting Beachwood, OH

11th October 2013

TG 142:

The Good, the Bad

and the Ugly

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Introduction Linac QA tolerance changes from TG 40

to 142

Linac QA new tests in TG 142

On board imaging QA in TG 142

CT Sim TG 66

Phantoms and software

for imaging QA

QA record software

Why TG 142 1994 TG 40 to 2009 TG 142

2nd year University to 2nd year as a medical Physicist

New technology – both hardware and delivery

MLC

Dynamic wedges

EPID & CBCT

Gating

IMRT, SBRT

Why talk about this now? ODH A Godley, Penn-Ohio River Valley 2013

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3D, IMRT and SBRT

Tighter limits for IMRT and SBRT

When does a machine fall under IMRT or

SBRT tolerances? 50% of cases? 1 case?

If it is capable?

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Flatness and Symmetry

Drop from 2 to 1%

From baseline, not absolute values

Beware of sign

+1% to -1% is out of tolerance

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Weekly tests

Quantitative MLC test

Suggests Picket Fence

Is this quantitative?

Is this necessary if you do patient specific

IMRT QA?

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Daily QA additions

Check-out run for one dynamic wedge

angle

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Extras

Gating

Laser guard

Stereotactic accessories

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Table V: MLC Monthly

Setting v radiation field

MLC rather than jaw

Backup diaphragm setting (Elekta)

Leaf travel speed

Necessary if no VMAT or dynamic delivery?

Picket fence @ 4 cardinal gantry angles

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Table V: MLC Annual

Transmission

Does this change?

Leaf position repeatability

MLC spoke shot (as opposed to jaw)

Segmental and Moving Window IMRT

Covered by IMRT QA?

Tolerances look to be from Varian

acceptance

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What’s in a name?

You could call your tests what you want in

your QA documents

Valdir’s zany MLC test

Make sure you associate your test with the

TG-142 test

Leaf position accuracy (IMRT)

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EPID based QA

Picket fence

Radiation versus light

Leaf speed

Flatness and Symmetry

Imaging

Patient specific

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Imaging

Additional QA workload

Simplified by all-in-one phantoms and

analysis software

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kV and MV planar image quality

Uniformity and Noise

Spatial Resolution Baseline

Contrast

Scaling

Imaging and treatment coordinate

coincidence @ 4 cardinal angles

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MV Phantoms

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kV Phantoms

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3D IGRT

Geometric distortion

Spatial resolution

Contrast

HU Constancy

Uniformity and noise

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3D IGRT Phantoms

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Isocenter coincidence

kV/MV

2D

Crosshair

3D

BB phantom

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Tomo, ExacTrac & CyberKnife

ExacTrac image quality

Difficulty to align phantom to imaging plane

Tomo

Skip iso/coordinate test?

CyberKnife

Isocenter coincidence?

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TG 66 CT sim QA

Lasers – internal versus external

Gantry tilt

Sensitivity profile width (semi-annually)

Annual – repeat tests for all kVp used

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Imaging Software

XVI/Syngo/OBI…

ImageJ, Paraview, Slicer – Self analysis

DoseLab

PIPsPro

RIT113

ImagePro

epidSoft

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QA records

Record that the QA was done

Repeat failed tests

Record final result

Record that issue investigated

OK to treat?

Test again after resolving issue

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QA monitoring software

Most of imaging tolerances are “Baseline”

Use trending to establish baseline and watch

for drifts

Also use records to determine whether

TG-142 tolerances and frequencies are

relevant for your linacs

Adapt your policies to reflect your experience

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QA software features Status page

Upcoming/overdue QA

Failed QA

Email warnings

Machine downtime records

Database

Comparison to anonymous online database

List of TG-142 and TG 66 tests

Interface with dosimetry devices

Monitor electrometer/chamber calibration A Godley, Penn-Ohio River Valley 2013

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