discovering quality in radiotherapy through transmission ... · is delivery qa beneficial? 1who...
TRANSCRIPT
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Discovering quality in radiotherapy through transmission detection
Mark Geurts, Researcher and Adjunct ProfessorUniversity of Wisconsin, Madison, USA
January 20, 2018
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Presentation outline
1. Introduction to University of Wisconsin
2. Review goals of patient-specific Quality Assurance
3. Explore role of transmission detection in QA
4. Evaluation of the ScandiDos Delta4 Discover
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Author Disclosure
• ScandiDos AB and HGPT funded travel to this meeting
and provided an honorarium
• The University of Wisconsin is a Center of Excellence
for ScandiDos products
• Images in this presentation are from delta4family.com
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University of Wisconsin, Madison
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UW medical physics history
John Cameron
Thermo-Luminescent Dosimetry (TLD)
Bone densitometry
Frank Attix
Spencer-Attix cavity theory
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UW medical physics history
Charles Mistretta
Digital Subtraction Angiography (DSA)
Vascular imaging
Thomas “Rock" Mackie
Pinnacle treatment planning system
TomoTherapy treatment system
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UW Radiation Oncology by the Numbers
Delivery
• 4 Varian
• 3 TomoTherapy
• 2 Elekta HDR
• 1 ViewRay
Planning
• RayStation
• Pinnacle
• Eclipse
• TomoTherapy
• Oncentra
Quality Assurance
• 5 Delta4
phantoms
• Mobius3D
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Delta4 history at the UW
• First unit commissioned in 2008
• Established as primary tool in 2012
• Upgraded to Delta4+ in 2016
• All UW centers now use Delta4
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UW IMRT QA policy
• Performed prior to treatment start, or
before 3 fractions/10% on transfers
• >95% data points must pass 3%/3 mm
global Gamma, using 20% threshold
• Median absolute dose < 3%
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Delta4 performance
• 2135 clinical plans since 2012
• Pass rate (3%/3mm): 96.3%
• Mean pass rate: 98.9%
• Absolute dose: 0.2% ± 1.3%
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Delta4+ upgrade
• Pass rate increased from
95.8% to 98.8%
• Standard deviation
decreased 1.4% to 1.0%
• No service in 2 years
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Goals of Patient Specific QA
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How safe is radiotherapy?
• WHO survey from 1976-2007
identified 3125 incidents1
• Patients died in 38 of them
• Other studies2 report error rates
between 0.1% to 4.7%
1WHO Radiotherapy Risk Profile (2008). www.who.int2Ford (2009). IJROBP 74:852-8
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Radiation therapy complexity
Huq (2016). Med Phys 43: 4209-62
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What is patient specific QA?
Quality Management
Quality Assurance
Machine QA Patient Specific QA
Pre-treatment Review
Delivery QAOn-
treatment Review
Quality Control
• Quality controls force the
desired level of quality
• Quality assurance
demonstrates a level of
quality for a process
American Society for Quality. asq.org
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Is delivery QA beneficial?In house ILS found delivery QA only detected 1.4% of all incidents:
Ford (2012). IJROBP 84: e263-9
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Is delivery QA beneficial?
1WHO Radiotherapy Risk Profile (2008). www.who.int2Gopan (2016). Med Phys 43: 5181-7
• WHO1 found 10% of all errors
occurred during treatment
delivery, 9% in data transfer
• In a study of SAFRON
events2, 23 of 81 (28%) had
incorrect field parameters
(angle, MU, wedge, etc.)
PlanningCommissioning
Delivery
Data Transfer
Source of Incident
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Plan quality sensitivity to delivery error
Fredh (2013). Med Phys 40: 031716
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Plan quality sensitivity to delivery error
Arumugam (2016). Physica Medica 32: 1238-44
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Recent surveys of medical physicists
Yes
No
Have you ever changed a plan based on IMRT QA?
On every
patient
Routinely
Not at all
Is absolute dose measurement necessary?
www.surveymonkey.com
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Transmission Detection QA
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What Is Transmission QA?
• Transmission QA systems place
an array of detectors between
the collimated beam and patient
• They allow intra-fraction
measurement of machine
parameters during treatment
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Strengths and Weaknesses
Strength Weakness
Real time QA measurement Difficult to compare to TPS
Independent of treatment system Low energy discrimination
Output, gantry angle, and collimation Surface dose, beam quality affected
Accurate MLC position verification*
*some systems
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Transmission vs. exit dosimetry
• 21st Century Oncology
evaluated 6.4 million EPID
exit doses across 84 centers
• 13% to 26% of all images
failed using 3% or 5% criteria50%
60%
70%
80%
90%
100%
H&NPelv
isBrea
stLu
ng
Prostat
e
Average Weekly Portal Pass Rate
Olivera et al. (2016) www.standardimaging.com
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What about log file analysis?
Several groups have discovered errors not caught by log file:
Agnew (2014). Phys Med Bio 59: N49-63
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What about log file analysis?
Neal (2016). Med Phys 43: 2933-5
Several groups have discovered errors not caught by log file:
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What about log file analysis?Several groups have discovered errors not caught by log file:
Rowshanfarzad (2015). Br J Radiol 88: 20140581
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Transmission detector comparison
*6 MV, 10x10
Li (2016). JACMP 17: 235-44
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ScandiDos Delta4 Discover
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Delta4 design
• 4040 p-type diodes with 1 mm active diameter
• Active area 25 x 20 cm at isocenter
• Diode spacing 1.6 (2.5) mm along MLC, 3.2 (5) mm against
• Overall system thickness 23 mm
Li (2016). JACMP 17: 235-44
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Delta4 Discover evaluation
Parameters
• Transmission
• Surface dose
• Beam quality
• Beam profile
• Output sensitivity
• IMRT reproducibility
• MLC error sensitivity
References
• Riley (2011). Med Phys 38: 3534
• Li (2016). JACMP 17: 235-44
• Saenz (2016). Med Phys 43: 3539
• Hoffman (2016). Med Phys 43: 3538
• Gonod (2017). Phys Med 44: 30
• Cheung (2017). PRO 7: e559-67
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Transmission
6 MV 10 MV 15 MV 18 MV Reference
0.989 0.993 Li (2016). JACMP 17: 235-44
0.988 0.993 Saenz (2016). Med Phys 43: 3539
0.985 Gonod (2017). Phys Med 44: 30
0.983 0.986 0.988 Hoffman (2016). Med Phys 43: 3538
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Surface dose
Author Cheung Li
Field (cm2) 10x10, 40x40 4x4, 10x10, 30x30
SSD (cm) 80, 100 90
Energy (MV) 6, 10 6, 15
Detector OSLD Diode
Result 10 x 10 40 x 40
80 +35% +63%
100 +4% +32%
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Beam quality
Author Hoffman Cheung Li Saenz
Field 1x1, 30x30 3x3 to 40x40 4x4 to 30x30 10x10
SSD 80, 100 90
Energy 6, 10, 15 6, 10 6, 15 6, 18
PDD 1% (> 2.5 cm)1.2% (100)
3% (80)
PDD(10):
-0.5%
PDD(10):
-0.7% (6)
+0.6% (18)
Dmax
4 mm (100)
8 mm (80)1.2 mm
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Beam profile
Author Hoffman Cheung Li
Field (cm2) 30x30 3x3 to 40x40 30x30
SSD (cm) 80, 90, 100 90
Energy (MV) 6, 10, 15 6, 10 6, 15
Result 1.25%2.6% (100)
6.3% (80)
Flatness -0.3%
Symmetry +0.5%
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Output sensitivityAuthor Li Saenz
MU error +1 to +5% -5 to +5%
Modality Static MLC field Static MLC field
Result
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IMRT reproducibility
Author Hoffman Gonod
Modality VMAT VMAT
Plan type Prostate Cervix, Head and Neck
Frequency Measurements over 9 days
Metric Gamma pass rate (3%/3mm)
StandardDeviation
0.5% 1.1-1.5%
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MLC error sensitivity
Author Li Saenz
Modality Static MLC Prostate VMAT Conformal arc
Leaf error 1-5 mm 0.5-5 mm 0-4 mm
Sensitivity 0.7 mm 1.2 mm
Result
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Combination with Delta4 Phantom
0
1
2
3
Discover Phantom+
Discover
Phantom+
Phantom+
Phantom+
Discover
Discover
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Error sensitivity relative to Delta4 Phantom
Riley (2011). Med Phys 38: 3534
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3DCRT evaluation
Without a Delta4 Phantom measurement, Discover can still measure
and compare to the DICOM RTPLAN:
• Monitor Units
• MLC position
• Gantry angle
• Collimator angle
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Anatomic evaluation
• Delta4 results can be used to
reconstruct dose to the planning CT
• Several groups have investigated:
Hu (2013). Med Phys 40: 213
Stambaugh (2014). JACMP 15: 169-180
Hauri (2014). JACMP 15: 181-90
Crockett (2015): Med Phys 42: 3411-2
Bängtsson (2016). Med Phys 43: 3370-1
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Thank you for your time