acceptance testing, commissioning and routine qa of the ... · acceptance testing, commissioning...
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Acceptance testing, commissioning and routine QA of the Varian TrueBeam
Richard Popple
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Disclosure
• UAB has Varian research contracts • Honorarium from Varian
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Not your father’s Chevy…
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Not your father’s Chevy…
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Not your father’s Chevy…
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Not your father’s Chevy Linac…
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TrueBeam – distinquishing characteristics • Completely digital control system • Waveguide and filter design allows 5 flattened
photon energies up to 20 MV. • Electron scattering foils are of a new design. • Implements 6 MV and 10 MV flattening filter free
(FFF) beams that provide dose rates up to 2400 monitor units per minute.
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Possible Benefits of a FFF
• Efficiency • More accurate beam modeling due to decreased
head scatter • Decreased leakage and dose outside field
The study showed that removing the filter increased the dose rate on the central axis by a factor of 2.31 (6 MV) and 5.45 (18 MV) at a given target current. Because the flattening filter is a major source of head scatter photons, its removal from the beam line could reduce the out-of-field dose.
Vassiliev ON, Titt U, Kry SF, Pönisch F, Gillin MT, Mohan R Med Physics 2006 vol. 33 (4) pp. 820-7
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Unflattened Beam Has a Lower Risk of Secondary Tumors
Cashmore J, Int J Radiat Oncol Biol Phys. 2011
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Beam Profile – Flattening Filter
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Depth Dose with Flattened Beam
2004 Phys. Med. Biol. 49 1535
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Calibration
• No difference for FFF • Polarity and recombination corrections small
Energy Dose rate Ppol Pion
6X 600 1.000 1.004
15X 600 1.000 1.005
6X FFF 1400 1.000 1.006
10X FFF 2400 1.000 1.013
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Calibration
Kry SF, Popple R, Molineu A, Followill DS. Ion recombination correction factors (P(ion)) for Varian TrueBeam high-dose-rate therapy beams. J Appl Clin Med Phys. 2012 Nov 8;13(6):3803. doi: 10.1120/jacmp.v13i6.3803. PubMed PMID: 23149774.
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Calibration
Kry SF, Popple R, Molineu A, Followill DS. Ion recombination correction factors (P(ion)) for Varian TrueBeam high-dose-rate therapy beams. J Appl Clin Med Phys. 2012 Nov 8;13(6):3803. doi: 10.1120/jacmp.v13i6.3803. PubMed PMID: 23149774.
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Calibration – use Pb foil for all FFF beams
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Calibration sanity check
-2
-1
0
1
2
3
4
5
6X FFF 400 M
U/m
in
6X FFF 1400 M
U/m
in
6X 600 M
U/m
in
10X FFF 400 M
U/m
in
10X FFF 2400 M
U/m
in
15X 600 M
U/m
in
Diff
eren
ce fr
om 6
X (%
)
Exradin A12EDR2MOSFET
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IROC Calibration check
• RPC OSLD measurement / Institution • 6X FFF = 0.99 • 10X FFF = 0.99
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Profile and depth dose correction for recombination
Measured x-ray distributions of 6FFF and 15FFF beams plotted against charged collected per beam pulse. Also plotted are the results from applying corrections for the ion chamber collection efficiency. The distributions were measured at 100 cm SSD with the 0.1 cm3 chamber at Dmax and biased with 300 V.
S Johnsen “Ion Chamber Collection Efficiency Considerations for Un-Flattened X-Ray Beams,” Med. Phys. 35, 2770 (2008)
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Profile and depth dose correction for recombination
Measured 15 FFF x-ray depth-dose distribution and distribution resulting from corrections for ion chamber collection efficiency. Each curve is normalized to 100% at Dmax. Data is for a 0.1 cm3 chamber biased to 300 V; 10x10 cm2 field at 100 cm SSD.
S Johnsen “Ion Chamber Collection Efficiency Considerations for Un-Flattened X-Ray Beams,” Med. Phys. 35, 2770 (2008)
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FFF head scatter
Cashmore Phys Med Biol 2008
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FFF surface dose
Vassiliev et al. Phys Med Biol 2006
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Photon commissioning
• AAA Data requirements are the same • No additional data required for FFF
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10X FFF profile
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IROC VMAT Spine
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IROC Gated VMAT Lung
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IMRT QA results
-4 -3 -2 -1 0 1 2 3 40
10
20
30
40
50
60
70
Num
ber o
f cas
es
Difference (%)
Mean=0.7%s.d.=1.1%
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IMRT QA results
0 5 10 15 200
20
40
60
80
Num
ber o
f cas
es
Fraction with γ > 1 for 3%/3mm (%)
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Daily QA device
0 50 100 150 2000
1
2
3
4
5
6
7
8 x 107
MU
Bea
m C
heck
er P
lus
sign
al
← Saturation!
10F 2400 MupMin10F 400 MupMin
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Varian engineer fixing UAB TrueBeam
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Machine performance check
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Machine performance check
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AAPM TG-142
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Orthogonal kV images
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Orthogonal kV images
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Cone beam CT
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Cone beam CT
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MV image
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MV image
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MV image
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Gantry sag
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Difference between automatic and manual
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Automated QA Consortium
Richard Popple
Hania Al-Hallaq & Karl Farrey
Todd Pawlicki & Grace Kim
Jeremy Booth & Mario Perez
Vijeshwar Sharma & Sung Park
John DeMarco
Toby Eckhause, Don Roberts, Brett Schultz
& Jean Moran
Tim Ritter
TBD via Dan Low Courtesy Jean Moran
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Phase 1 QA Test Suite
Standardize tests and QA test suite so to evaluate the performance of TrueBeam linacs and compare our results across multiple institutions
Use both trajectory log files and EPID measurements
(a) (b)
Courtesy Jean Moran
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Example Fields of QA Test Suite
+ picket fence for VMAT with variable gantry speed, variable gantry speed and dose rate Both HDMLC and Millennium MLC supported
Courtesy Jean Moran
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Automated QA Analysis
Software analysis developed in MatLab primarily developed by Toby Eckhause (former post-doc)
Test suite takes ~15 minutes to deliver; 1 flood field + enter room once to setup phantom
All analysis from the original test suite is automated and results can be exported
Less than a minute to analyze all data
Courtesy Jean Moran
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Trajectory Log File & EPID Analysis
Leaf Position Deviation A (µm)
0 20 40
-10
-5
0
5
10 -6
-4
-2
0
2
4
6
-10 -5 0 5 101.4
1.5
1.6
1.7
1.8
1.9
2
Leaf A Position (cm)
Leaf
Dev
iatio
n S
tdev
( µm)
-10 -5 0 5 10-8
-6
-4
-2
0
2
4
Leaf A Position (cm)
Leaf
Pos
ition
Dev
iatio
n( µm
)
meanminmax
Test suite included all MLC monthly tests in Table V of TG 142, VMAT tests, plus imaging tests.
Analysis of Trajectory Log Files
Maximum difference for leaf position accuracy From Phase 1 of our project with 8 linacs measured over 6 months
Courtesy Jean Moran
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Questions?