Download Quality Assurance of Radiation Oncology Imaging

Quality Assurance of Radiation
Oncology Imaging Systems
Karl L. Prado, Ph.D.
Department of Radiation Physics,
University of Texas MD Anderson Cancer Center
Houston, Texas
Mexican Federation of Medical Physics Organizations,
Southwest Chapter of the American Association of Physicists in Medicine,
Queretaro, Mexico, March, 2007
Introductory Remarks:
Training and Quality Assurance
„
Imaging Physics for the Therapy Physicist
„
„
An introduction to the technology of digital
imaging in radiation oncology: its
fundamentals, current clinical utilization, and
initial Quality Assurance effort
Li and Hendee. JACR (4), 40, 2007:
Radiation Oncology Physicists Will Need to
Better Understand Medical Imaging
„
… “A major effort is required for radiation oncology
physicists to raise the quality assurance of image
guidance to a level comparable with that achieved
in the maintenance of dosimetric performance.” …
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Acknowledgement of
Collaborators
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Faculty - Clinical
Physics
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Peter Balter
Tina Briere
Rajat Kudchadker
Patricia Lindsay
Rachel Liu
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Engineering
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Tom Diel
Jermaul Prince
Chad Fikes
Sean Swiedom
Quality Assurance
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Robert Session
Craig Martin
Andrea Robason
Rationale for Radiation
Oncology Imaging System QA:
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Successful targeting
of tumor volumes
depends greatly on
optimized imaging
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Target and margin
definition
Target position
determination and
verfication
From:
ICRU News, Dec. 1999
2
Rationale 1:
Accurate Target Definition
SM
The IGTV: Internal
Margin Definition
CTV
IG’TV
Target Volumes
and Internal and
Setup Margins
Rationale 2:
Verification of Treatment Delivery
Patricia Lindsay, Ph.D., Tina Briere, Ph.D.
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Rationale 2: Verification of
Treatment Delivery
Vertebral Body IMRT:
Plan and Verification
QA of Radiation Oncology
Imaging Systems: Overview
„
Current Imaging Technologies in
Radiation Oncology
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„
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Fundamentals
Clinical Uses of Technology
Imaging System Quality Assurance
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Imaging system performance areas and
Quality Control (QC) parameters
QC procedures and tools
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Current Imaging Technologies
in Radiation Oncology
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Technology addressed:
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PET/CT
Computed Tomography
(CT)
Electronic Portal Imaging
Devices (EPIDs)
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MV
MV systems
kV systems
Computed Radiography
(CR) Systems
CR
kV
CT in Radiation Oncology
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CT Technology
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Multi-Slice (4, 8, 16, 64)
Spiral Pitch
Imaging requirements differ
from Diagnostic Imaging
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Patient group
Purpose of imaging
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Target definition and
localization, dose
calculation
D(r ) =
∫
r'
μ
(r ' ) × Ψ (r ') × Κ (r ' → r )
ρ
Imaging procedure
Bore size, couch, lasers,
software
Optimized CT imaging
protocols
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Optimized Imaging Protocols
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Optimization of
CT imaging
protocols for:
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High contrast
resolution
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Low contrast
resolution
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CATPHAN CTP528
line pair module
1% low contrast
CTP515 module
Presence of
artifacts
Optimized protocols for 2.5-3.0
mm slice thickness images
Unit
Pitch
Detector
Configuration
Philips MX8000
0.688
16 × 0.75
Philips AcQSim
1
1 channel ×
3mm
GE LS16
1.375
16 × 1.25
GE LS RT16
0.938
16 × 1.25
GE LS RT
0.75
4 × 1.25
Rachel Liu, Ph.D., et. al., AAPM Abstract (submitted), 2007
Electronic Portal Imaging
Devices - EPIDs (DR Systems)
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Current generation EPIDs
use Flat Panel Amorphous
Silicon Arrays (aSi)
A large glass plate is divided
into an array of 1 million
photo diodes/capacitors
Light is created in a detector
(scintillation) layer
Light is converted to charge
by the photodiode
The charge is digitized by a
collection A/D converters
X-rays
light
Scintillator
Photodiodes
A/D A/D A/D A/D
A/D A/D A/D A/D
A/D
Converters
Peter Balter, Ph.D.
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Amorphous Silicon Detector
Cross Section of an A-Si Detector Pixel
copper metal plate 1mm
Phosphor 0.4 mm
e-
photodiode λ
MeV x-ray
x-ray converter
a-Si:H 1.5um
glass substrate 1mm
TFT switch
scatter photon
• Conversion of x-ray to optical signal
• Conversion of optical signal from the phosphor to charge
• Storage of charge on pixel (photo-diode) capacitance
13 wjw 12/01
From: Varian
Medical Systems
Flat Panel a-Si Arrays
From: Digital Radiographic Technology, John Yorkston, Ph.D.
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Computed Radiography
Systems
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Plate scans
down
Aperture
43 cm
Laser
Stimulated Emission
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A Photostimulable
Storage Phosphor (PSP)
plate stores a ‘latent
image’ (analogous to
film)
The PSP plate is
subsequently “read” by
detecting the emissions
produced by laser
stimulation
Peter Balter, Ph.D.
Computed Radiography (CR)
Systems
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Image Formation
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Photostimulable
Storage Phosphors
(PSPs)
Latent image is
created at F-centers
(electron metastable states)
produced by x-rays
AAPM Report 93
8
Computed Radiography
Systems
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Image Readout
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Plate is scanned by laser
along a slit
Luminescent signal
captured by PMT
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Intensity is proportional
to dose
Position determined by
laser position
Plate is ‘erased’ by
emptying meta-stable
traps using high-intensity
light
AAPM Report 93
QA of Radiation Oncology
Imaging Systems: Overview
„
Current Imaging Technologies in
Radiation Oncology
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„
Fundamentals
Clinical Uses of Technology
Imaging System Quality Assurance
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„
Imaging system performance areas and
Quality Control (QC) parameters
QC procedures and tools
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Virtual Simulation and
Treatment Planning
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Target definition,
organ segmentation,
beam and isocenter
determination
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Visualization,
contouring, multimodality fusion
Beam definition and
isocenter localization
„ DRRs
Verification of Treatment
Delivery: Traditional Methods
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MV (and now
kV) Images
Anatomy and
reticule based
With digital
imaging can use
imageenhancement
tool
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Histogram
Equalization
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Verification of Treatment
Delivery: CT-Based IGRT
Courtesy of: Lei Dong, Ph.D., and Associates
Newer Image Guidance
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AP
“2D” Match
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Image (kV)
registration to
plan DRR
Couch shift
computed
(and can be
applied)
Lat
DRR
kV
Varian
Tina Briere, Ph.D., Patricia Lindsay, Ph.D.
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Newer Image Guidance
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Fiducial-Marker
Match
DRR
kV
Isoloc
Tina Briere, Ph.D., Patricia Lindsay, Ph.D.
QA of Radiation Oncology
Imaging Systems: Overview
„
Current Imaging Technologies in
Radiation Oncology
„
„
„
Fundamentals
Clinical Uses of Technology
Imaging System Quality Assurance
„
„
Imaging system performance areas and
Quality Control (QC) parameters
QC procedures and tools
12
Imaging System Performance
Areas and Quality Control
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Image Quality and Image Quality
Measures
Geometric Accuracy Requirements
Regulatory Requirements
Image Quality Measures
In general:
„ Density (darkness)
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Contrast (Low)
Sharpness
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Spatial Resolution (MTF)
Signal/Noise (SNR)
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Dose relationship
Latitude
Noise
Artifacts
For digital images:
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Uniformity
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Linearity
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Spatial distortion
Lag
Image processing
Display
……
Based on: AAPM Monograph 30, 2004
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Image Quality / Measures
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Uniformity
High Contrast
Spatial
Resolution
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QC-3
MTF or LSF
Low Contrast
Resolution
Noise
(References)
Artifacts
PIPSpro
Las Vegas
Geometric Accuracy
Requirements
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Margins and relationships between
treatment plan (1), treatment-unit (2), and
imaging system (3) isocenters
(3)
(2)
(1)
RadAc
Winston-Lutz Test
(2)
Rajat Kudchadker, Ph.D.
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Imaging Systems Regulatory
Requirements
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State Regulations
25 TEXAS ADMINISTRATIVE CODE, §289.227, “Use of
Radiation Machines in the Healing Arts”
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General Requirements
Technique charts, operating and safety procedures;
operator / medical physicist credentialing, …
Radiographic entrance exposure limits
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Radiographic / Fluoroscopic
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CT
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Beam quality: half-value layer, kVp accuracy
Beam limitation: x-ray field vs. indication
Exposure reproducibility; linearity……
Radiation output of the CT system (CTDI)
Additional requirements applicable to CT x-ray
systems……
CT Quality Control (1)
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Baseline:
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Daily QC
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Manufacturer’s specifications
References: AAPM TG Reports
66 & 39
High Contrast; Spatial integrity
Low Contrast resolution
Uniformity
CT ring artifact (each channel)
Monthly QC
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Localization laser accuracy
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Lap laser movement accuracy
CT number accuracy
……
Rachel Liu, Ph.D.
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CT Quality Control (2)
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Monthly QC (cont.)
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Laser Position Scale
Laser (external) alignment
with imaging plane …
Annual QC
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CTDI measurements
Tube output linearity
Radiation Profile
Image quality evaluation:
uniformity, CT number
accuracy, resolution, slice
sensitivity profile, etc.
Couch movement accuracy
……
10-cm CT Ion Chamber
Radcal, 9095 Multi-Purpose Analyzer
EPID and OBI Quality Control
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MV / kV Imagers:
Requirements
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Baseline
Daily QC
Monthly QC
Annual QC
Varian
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OBI Quality Control
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kV Imagers:
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Baseline
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Daily QC
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Acceptance Specs.
Baseline
performance
Functional:
Isocenter
verification with shift
Monthly QC
Annual QC
Rajat Kudchadker, Ph.D., Robert Session, B.S.
QBI Quality Control
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Monthly QC
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Isocenter coincidence
(increased precision)
Image quality:
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Contrast (Leeds)
Resolution (Line pair)
Annual QC
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Regulatory x ray
Image quality
Safety, mechanical
QCkV-1
Leeds
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EPID Quality Control
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MV Imagers:
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Las Vegas
Baseline
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Acceptance
Specs.
Baseline
performance
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Daily QA
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Monthly QA
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Re-acquire dark
and flood fields
Functional
Image Quality
Annual QA
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QC-3
Mechanical /
Safety
Image Quality
Karl Prado, Ph.D., Andrea Robason, B.S.
CR System Quality Control
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Baseline
Daily QC
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Monthly QC
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Startup calibration (self
test)
Cleaning imaging plates,
cassettes, scanners
Image quality …
Annual QC
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Uniformity
Resolution
Distortion
Artifacts …
15%
Rachel Liu, Ph.D., Craig Martin, B.S.
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Data Flow
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Can be complex
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Reliance on IT
Image storage and
retrieval
Multi-vendor
environment
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Security:
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In-house solutions
Firewalls
Security updates
…
Ron Zhu, Ph.D., et al
References: General
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Specifications, Performance Evaluation,
and Quality Assurance of Radiographic
and Fluoroscopic Systems in the Digital
Era. AAPM Medical Physics Monograph
No. 30, 2004.
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Fundamentals: Samei, E. Saunders, R. The
Nature of the Digital Image.
Flat Panel Imagers: Yorkston, J. Flat Panel DR
Detectors for Radiography and Fluoroscopy.
CR Systems: Seibert, J. Computed
Radiography Technology 2004.
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References (Continued)
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CT Simulation
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AAPM Task Group 66. Quality
Assurance for Computed
Tomography Simulators and the
Computed-Tomography-Simulation
Process. Med. Phys. 30 (10), 27622792 (2003)
References (Continued)
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Electronic Portal Imaging
Systems
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AAPM Task Group 58. Clinical
Use of Electronic Portal Imaging.
Med. Phys. 28 (5), 712-737
(2001)
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References (Continued)
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Computed Radiography (CR)
Sytems
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AAPM Task Group 10. Acceptance
Testing and Quality Control of
Photostimulable Storage Phosphor
Imaging Systems. AAPM Report
Number 93, 2006.
„
http://www.aapm.org/pubs/reports/
References (Continued)
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Radiation Oncology Imaging Systems
Quality Assurance
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Yoo, S. … A Quality Assurance Program
for the On-Board Imager. Med. Phys.
33, (11), 4431-4447, 2006
Rajapakshe, R. … A Quality Control Test
for Electronic Portal Imaging Devices.
Med. Phys. 23 (7), 1237-1244, 1996
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References (Continued)
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Radiation Oncology Quality Assurance
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http://www.oncologymeetings.org/
QA of Radiation Oncology Imaging Systems
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Jaffray, D. QA Program for Radiographic, Fluoroscopic,
and Cone-Beam CT Image Guided RT.
Balter, J. QA for Radiographic On-Line and Off-Line
Localization.
Imaging System QA: Summary
„
Overview of digital imaging systems
in Radiation Oncology
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Still much to learn
CT, EPID, and OBI Systems
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Principles, Practice
Quality Assurance Program
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Initial Effort
To be continued …
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Thank you!
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