Establishing equipment performance
standards: two approaches
Establishing equipment performance
standards: two approaches
Outline
Peter Dunscombe, Ph.D.
University of Calgary/
Tom Baker Cancer Centre
1.The Issues
2.A Consensus Approach
3.An “Objective” Approach
AAPM Annual Meeting, 25th July 2007
4.Conclusions
The Issues
Establishing equipment performance
standards: two approaches
The Issues
Outline
1.The Issues
2.A Consensus Approach
The requirements for Quality Assurance in Radiation
Therapy are increasing faster than the availability of
resources
3.An “Objective” Approach
4.Conclusions
1
The Issues
The Issues
What’s changing?
What’s changing?
•Equipment and clinical protocols are becoming much
more complex.
•Equipment and clinical protocols are becoming much
more complex.
•There is increasing recognition that we need to QA
processes as well as infrastructure.
The advent of Intensity Modulated Radiation Therapy has
had a dramatic impact on the demand for QA.
•There is a greater acknowledgement of the potential for
major failures.
Image Guided Radiation Therapy is doing the same.
The Issues
The Issues
What’s changing?
What’s changing?
•There is increasing recognition that we need to QA
processes as well as infrastructure.
•There is a greater acknowledgement of the potential for
major failures.
In both the Glasgow and Epinal incidents the
infrastructure performed as it should but the processes
failed.
TG 100 is specifically addressing this issue through a
Failure Modes and Effects Analysis.
2
The Issues
The Issues
The Scope of this Presentation
The Scope of this Presentation
•A look at two approaches to establishing performance
standards for radiation therapy infrastructure.
•A look at two approaches to establishing performance
standards for radiation therapy infrastructure.
That means:
That means:
no process QA
just good old fashioned QC like we’
we’ve
done for years.
no FMEA
But:
particularly due to workload pressures we
need to review our traditions.
A Consensus Approach
Establishing equipment performance
standards: two approaches
Outline
The Development of Quality
Control Standards for Radiation
Therapy Equipment in Canada
1.The Issues
2.A Consensus Approach
Peter Dunscombe, Harry Johnson, Clement Arsenault,
George Mawko,
Mawko, JeanJean-Pierre Bissonnette and Jan Seuntjens.
Seuntjens.
3.An “Objective” Approach
4.Conclusions
J Appl Clin Med Phys 8 (2007) 108-118
3
A Consensus Approach
A Consensus Approach
Background
The Canadian Association of Provincial Cancer Agencies
initiated a process aimed at harmonizing quality assurance
activities in radiation treatment programs across Canada.
The development of equipment performance standards was
delegated to the Canadian Organization of Medical
Physicists (COMP).
A Consensus Approach
Philosophy and Scope
•Radiation safety has not been specifically included. To do
so would require updating the documents each time federal
or provincial regulations were changed.
•However, some of the more straightforward tests
performed on a daily basis were included for completeness.
Philosophy and Scope
•The documents should focus on the standards themselves
and not include descriptions of how the tests are
performed.
•It is assumed that physicists who perform, or supervise the
performance of, the tests possess an appropriate level of
knowledge.
A Consensus Approach
Philosophy and Scope
•The standards documents were intended to be brief and
unambiguous.
•By distributing them through a website, they could be
readily updated as experience with new techniques is
gained.
4
A Consensus Approach
Document Design
To maintain focus and unambiguity, a generic document
format was adopted.
The sections are as follows:
•Introduction – largely generic
•Performance Standards – generic
•System Description – custom
•Acceptance Tests and Commissioning – largely generic
•Quality Control of Equipment – largely generic
•Documentation – generic
•Table of QC Tests – custom entries in a generic format
•References and Bibliography – custom
A Consensus Approach
Document Generation
•The source document was either specifically
commissioned or existing in some Canadian jurisdiction
(Ontario)
•The source document was reviewed by knowledgeable
Canadian medical physicists in the light of relevant
international publications.
•The source document was then reviewed by the Task
Group and reformatted to fit the generic style.
A Consensus Approach
Document Design
The generic Performance Standards section includes six
classes:
•Functionality,
•Reproducibility,
•Accuracy,
•Characterization and Documentation,
•Data Transfer and Validation
•Completeness.
A Consensus Approach
Document Approval
•The draft document was posted on www.medphys.ca for
consideration by the Canadian medical physics community
at large
•Comments were received and incorporated as appropriate.
•The document is approved by the Executive of the
Canadian Organization of Medical Physicists
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A Consensus Approach
A Consensus Approach
Results
Results
Designator
Test
Performance
Tolerance
Action
Daily
•Limited feedback from the Canadian medical physics
community
•Possible reasons:
• general agreement with content
• it’
it’s going to happen anyway
• documents to date closely reflect current practice
A Consensus Approach
DL1
Door interlock/last person out
Functional
DL2
Motion interlock
Functional
DL3
Couch brakes
Functional
DL4
Beam status indicators
Functional
DL5
Patient audio-visual monitors
Functional
DL6
Room radiation monitors
Functional
DL7
Beam interrupt/ counters
DL8
Lasers/crosswires
1
2
DL9
Optical distance indicator
1
2
DL10
Optical back pointer
2
DL11
Field size indicator
1
2
DL12
Output constancy - photons
2%
3%
DL13
Dynamic wedge factors
1%
2%
DL14
Output constancy - electrons
2%
3%
Functional
3
A Consensus Approach
Results
Results
Currently Approved Standards
Standards awaiting approval or under development
• Electronic Portal Imaging Devices
•Conventional Radiotherapy Simulators
•kiloVoltage Therapy Units
•Medical Linear Accelerators
•Cobalt Therapy Units
•Multileaf Collimators
•Stereotactic Radiosurgery/Radiotherapy
•Brachytherapy Remote Afterloaders
•Major Dosimetry
•CT Simulators
•LDR Prostate Brachytherapy
•Treatment Planning Systems
•Data Management Systems
•Linac Integrated Imaging Systems and CBCT Simulators
•Respiratory Management Systems
•IMRT
6
A Consensus Approach
Conclusions
• the largely generic format facilitates document
development
• consensus takes time
• limited feedback from the Canadian community was
received
• the format makes compliance easy to monitor for
accreditation purposes, for example
• onon-going upup-dating is required
An “Objective” Approach
Towards an objective evaluation
of tolerances for beam modeling
in a treatment planning system
Alejandra Rangel, Nicolas Ploquin, Ian Kay
and Peter Dunscombe
Establishing equipment performance
standards: two approaches
Outline
1.The Issues
2.A Consensus Approach
3.An “Objective” Approach
4.Conclusions
An “Objective” Approach
Background
•The performance of a convolution/superposition based
treatment planning system depends on the ability of the
algorithm to accurately account for physical interactions
taking place in the tissue and key components of the linac
head and on the accuracy of the photon beam model.
•Generally the user has little or no control over the
performance of the algorithm but is responsible for the
accuracy of the beam model within the constraints imposed
by the system.
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An “Objective” Approach
An “Objective” Approach
Rationale
Materials
• beam modeling and validation takes time
• Pinnacle®
• models are rarely perfect
• 6 and 15MV photon beam models
• plan quality could be enhanced and efficiencies gained if
we knew the relative importance of the different
characteristics of a beam model
• 28 clinical CT scans and associated plans
• 4 field conformal prostate
• 2 field tangential breast
• 3-4 field conformal lung
• 3-8 field conformal brain
An “Objective” Approach
An “Objective” Approach
Materials
Methods
• reference models chosen for 6 and 15MV photon beams
• reference models perturbed “independently”
independently” in each of
the Venselaar based regions (water phantom)
•six perturbed beam models were developed for each of the
six profile regions
after Venselaar et al. Radiother. Oncol. 60 (2001) 191-201
8
An “Objective” Approach
An “Objective” Approach
Methods
Methods
• clinical plans were run with the perturbed models
• 28 CT based plans x 6 perturbed models per region x 6
regions ~ 1000 plans
• Equivalent Uniform Doses of targets and organs at risk
were calculated
An “Objective” Approach
An “Objective” Approach
Results
4
1
0
-1
-2
-3
2
1
0
-1
1:Descending Depth Dose
2:Build-up
3:Horns
4:Tail
-4
-2
-3
Prostate CTV
3
1:Descending Depth Dose
2:Build-up
3:Horns
4:Tail
1
0
2
1
0
-1
-2
5:Penumbra
-3
6:Field width
-2
5:Penumbra (bladder)
5:Penumbra (rectum)
6:Field width (bladder)
6:Field width (rectum)
-3
-4
-4
-8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8
Percent Deviation (%)
Prostate OARs
3
2
-1
-4
-8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8
Percent Deviation (%)
4
4
Rectum
C ha nge in EU D (G y)
2
3
P ercent Cha nge in EU D (% )
Prostate CTV
P erc ent C h ange in EU D (% )
Percent C hange in E UD (% )
4
3
Results
-4
-3
-2
-1
0
1
2
Percent Deviation (mm)
3
4
-4
-3
-2
-1
0
1
2
3
4
Percent Deviation (mm)
9
An “Objective” Approach
An “Objective” Approach
Results
CTV (%)
Bladder (Gy)
Rectum (Gy)
8.0
3.5
7.0
3.0
4.0
Lung Plans
GTV (%)
3.5
Heart (Gy)
Lung (Gy)
6.0
3.0
5.0
2.5
4.0
2.0
3.0
1.5
5.0
2.5
4.0
2.0
3.0
1.5
2.0
1.0
2.0
1.0
1.0
0.5
1.0
0.5
0.0
0.0
0.0
1:Depth 2:Build up 3:Horns
Dose 2%
10%
3%
4:Tail
3%
4:Tail
3%
5:Penum 6:Field
2mm Size 2mm
Regions of the dose profiles
Regions of the dose profiles
An “Objective” Approach
An “Objective” Approach
Results
Rectum (Gy)
4.0
8.0
3.5
7.0
3.0
5.0
2.5
4.0
2.0
3.0
1.5
2.0
1.0
1.0
0.5
0.0
0.0
1:Depth 2:Build up 3:Horns
Dose 1.5% 7%
2%
4:Tail
3.5%
5:Penum
1mm
Regions of the dose profiles
6:Field
Size
0.5mm
6.0
Conclusions
4.0
Brain Plans
CTV1
Brainstem
3.5
CTV2
Opt chiasm
3.0
5.0
2.5
4.0
2.0
3.0
1.5
2.0
1.0
1.0
A b so lu te C h an g e in E U D
(G y)
P e rc e n ta g e C h a n g e in
E U D (% )
6.0
Bladder (Gy)
Pe rcen tag e C h an g e in
EU D (% )
Prostate Plans
CTV (%)
A b s o lu te C h a n g e in E U D
(G y )
8.0
7.0
If we define clinical objectives perhaps
we can work backwards to tolerances on
beam modeling
0.0
1:Depth 2:Build up 3:Horns
Dose 2%
10%
3%
5:Penum 6:Field
2mm Size 2mm
A bsolute C hang e in EU D
(Gy)
P ercentage C han ge in
EU D (% )
6.0
4.0
Percentage C hange in
EU D (% )
Prostate Plans
7.0
A b solute C han ge in EU D
(G y)
8.0
Towards an objective evaluation
of tolerances for beam modeling
in a treatment planning system
• depth dose and horns have the greatest impact on the
EUD of the target
• field size has the greatest impact on the EUD of the
organs at risk
0.5
0.0
0.0
1:Depth 2:Build up 3:Horns
Dose 1.5% 7%
2%
4:Tail
3.5%
5:Penum
1mm
6:Field
Size
0.5mm
Regions of the dose profiles
10
An “Objective” Approach
Conclusions
setting tolerances based on predicted clinical outcome, if
possible, is a more logical approach than setting tolerances
based on what is routinely achievable
Summary
Against a background of increasing demand for Quality
Assurance in Radiation Therapy we need to explore new
methods for establishing performance standards.
• a national consensus approach
• an approach linked to clinical outcome
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