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Andrew Godley
Joint Ohio River Valley
Penn-Ohio
Chapter meeting Beachwood, OH
11th October 2013
TG 142:
The Good, the Bad
and the Ugly
A Godley, Penn-Ohio River Valley 2013 2
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
3
A Godley, Penn-Ohio River Valley 2013 4
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?
A Godley, Penn-Ohio River Valley 2013 5
Flatness and Symmetry
Drop from 2 to 1%
From baseline, not absolute values
Beware of sign
+1% to -1% is out of tolerance
A Godley, Penn-Ohio River Valley 2013 6
Weekly tests
Quantitative MLC test
Suggests Picket Fence
Is this quantitative?
Is this necessary if you do patient specific
IMRT QA?
A Godley, Penn-Ohio River Valley 2013 7
Daily QA additions
Check-out run for one dynamic wedge
angle
A Godley, Penn-Ohio River Valley 2013 8
Extras
Gating
Laser guard
Stereotactic accessories
A Godley, Penn-Ohio River Valley 2013 9
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
A Godley, Penn-Ohio River Valley 2013 10
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
A Godley, Penn-Ohio River Valley 2013 11
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)
A Godley, Penn-Ohio River Valley 2013 12
EPID based QA
Picket fence
Radiation versus light
Leaf speed
Flatness and Symmetry
Imaging
Patient specific
A Godley, Penn-Ohio River Valley 2013 13
Imaging
Additional QA workload
Simplified by all-in-one phantoms and
analysis software
A Godley, Penn-Ohio River Valley 2013 14
kV and MV planar image quality
Uniformity and Noise
Spatial Resolution Baseline
Contrast
Scaling
Imaging and treatment coordinate
coincidence @ 4 cardinal angles
A Godley, Penn-Ohio River Valley 2013 15
MV Phantoms
A Godley, Penn-Ohio River Valley 2013 16
kV Phantoms
A Godley, Penn-Ohio River Valley 2013 17
3D IGRT
Geometric distortion
Spatial resolution
Contrast
HU Constancy
Uniformity and noise
A Godley, Penn-Ohio River Valley 2013 18
3D IGRT Phantoms
A Godley, Penn-Ohio River Valley 2013 19
Isocenter coincidence
kV/MV
2D
Crosshair
3D
BB phantom
A Godley, Penn-Ohio River Valley 2013 20
Tomo, ExacTrac & CyberKnife
ExacTrac image quality
Difficulty to align phantom to imaging plane
Tomo
Skip iso/coordinate test?
CyberKnife
Isocenter coincidence?
A Godley, Penn-Ohio River Valley 2013 21
TG 66 CT sim QA
Lasers – internal versus external
Gantry tilt
Sensitivity profile width (semi-annually)
Annual – repeat tests for all kVp used
A Godley, Penn-Ohio River Valley 2013 22
Imaging Software
XVI/Syngo/OBI…
ImageJ, Paraview, Slicer – Self analysis
DoseLab
PIPsPro
RIT113
ImagePro
epidSoft
A Godley, Penn-Ohio River Valley 2013 23
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
A Godley, Penn-Ohio River Valley 2013 24
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
A Godley, Penn-Ohio River Valley 2013 25
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
26
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