Patient Specific Quality Assurance
for IMRT and VMAT
based on Radiochromic Film Dosimetry
with EBT2/EBT3 Film
Sou-Tung Chiu-Tsao, PhD
Quality MediPhys LLC, Denville, NJ
Presentation at the New Jersey Medical Physics Society
Jun. 12, 2012
Disclosure Statement
• Consultant to Ashland Inc.
(Formerly ISP)
Background
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Safety and quality of radiation therapy
Machine equipment QA
Complex treatment modalities
Imaging devices
Immobilization/support devices
Skin dose issue
Complex Treatment Modalities
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SRS (Stereotactic Radiation Surgery, single fx)
SRT (Stereotactic Radiation Therapy, multiple fx)
SBRT (Stereotactic Body Radiation Therapy)
Helical Tomotherapy
IMRT (Intensity Modulated Radiation Treatment)
VMAT (Volumetric Modulated Arc Therapy)
IMRT
• Fixed gantry angle
• Constant output rate
• Multileaf collimator (MLC)
leaves move during the
treatment
• Non-uniform beam intensity
• Technique
– Sliding window
– Step and shoot
VMAT
• Arc delivery of
IMRT
• MLC leaf
motion
• Gantry
rotation
• Output rate
variation
Webb & McQuaid, PMB 2009; 54: 4345-4360.
VMAT/IMRT Prostate
VMAT
IMRT
30 50 70 90 100 105 %
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Evolving rapidly
MU ~ 300
Less treatment time
Output rate varies with angle
Rotating gantry
– Single arc, Multiple arc
– Partial arc, Split arc
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Established
MU ~ 600
More treatment time
Output rate remains fixed
Fixed gantry angle for each field
Patient Specific QA
• Consult, diagnostic data gathering
• Decision making on
– Prescription dose to target
– Tolerance doses to organs at risk (OAR)
• Treatment planning CT scan simulation
• Delineation of contours of target and OARs
• Treatment planning calculation
• Pre-treatment QA
• On-treatment, in vivo monitoring
• Post-treatment analysis
• Skin dose
Pre-Treatment QA
• 2D dosimetry
– Ion chamber array
– Diode array: MapCHECK
– Radiochromic film: EBT2, EBT3 film
– EPID
• 3D, 4D dosimetry
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Gel
Delta4 (2 perpendicular diode arrays )
ArcCHECK
4D Monte Carlo simulation
Planar Dose: Gamma Index
Solid: TPS
Dotted: EBT2 Film
Gamma index:
Distance difference:
Dose difference:
Low, Med Phys 2003; 30: 2455-2464.
DTA criterion: ∆d
Dose diff criterion: ∆D
Pre-Treatment QA Procedure: EBT2/3 Film
Import Plan via
DICOM
Flatbed
Scanner
Results
cGy
Export via
R&V System
Film
Expose
Phantom
Film Dosimetry
• Radiographic film, Kodak
– XTL, XV2, EDR2
• Radiochromic film, Ashland (Formerly ISP)
– XR-QA, XR-RV2, EBT, EBT2, EBT3, MDV3, HDV2
• Fine spatial resolution
• Darker shade with higher dose
EBT2 and EBT3 Films
Contains yellow marker dye
Color: yellow to green
Less sensitive to ambient light
EBT2
EBT3
Clear Polyester
- 50 mm
Adhesive Layer - 25 m m
Active Layer - 28 m m
Matte Polyester - 120 mm
- 175 m m
Matte Polyester - 120 mm
Clear Polyester
Asymmetric
Active Layer - 28 mm
Symmetric
Matte Polyester in EBT3 Film
Common Setup for IMRT QA
EDR2 Film
Measurement
probe for
absolute
point dose
EBT2/3 Film
Film for 2D
dose distribution
Solid Water
EBT2/3 Film in Phantom on Couch
EBT2/3 Film
in Coronal Plane
IGRT couch
EBT2/3 Film Dosimetry
• Technical Considerations
– Note model and lot #
– Note film orientation and alignment
– Control time between irradiation and scanning
– Environmental factors: humidity, temperature
– Store in dark envelopes
• Scanner influence, uniformity, and software
Tips for Scanning EBT2/EBT3 Film
for IMRT and VMAT QA
• Scan all films in the same orientation
Landscape or portrait orientation
• Place the film at the center of the scanner bed
• Practical spatial resolution for IMRT/VMAT QA
– 72 dpi, i.e. 0.35 mm per pixel
• Use 48 bit color mode, red, green, blue channels
• Use transmission mode
• Disable color correction feature
Epson 10000XL Flatbed Scanner
Landscape orientation of film on the scanner bed
Transparency
adapter
Coating direction
Scanning direction
Scanner bed
10000XL
10000XL
Epson 10000XL Flatbed Scanner
Portrait orientation of film on the scanner bed
Coating direction
Scanning direction
10000XL
EBT2/3 Film Image w/48 Bit Color Mode
EBT2/3 film RGB image
consists of 3 components
Separated into 3 images in red,
green and blue channels
Absorption Spectra of EBT2/3 Film
2.5
420 nm
636 nm
Absorbance
2.0
585 nm
1.5
After exposure of 2 Gy
1.0
0.5
Before exposure
0.0
350
400
450
500
550
600
Wavelength, nm
Courtesy: Dr. David Lewis
650
700
750
800
• Active component
– Signals in red
and green
channels
Absorbance
Absorption Spectra of EBT2/3 Components
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Visible Spectrum of Active Component
after Exposure
400
500
600
700
Wavelength, nm
Visible Spectrum of Marker Dye
3
Absorbance
• Marker dye
– Signal in blue
channel
Before exposure
2
After exposure to 50Gy
1
0
350
400
450
500
550
600
Wavelength, nm
Courtesy: Dr. David Lewis
650
700
Data Analysis Method
• Single channel method
– Red channel only
– Green channel only
– Blue channel only
• Triple channel method
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Red, green and blue channels
Removes film and scanner artifacts
Allows compensation for film thickness variation
Significantly improves the accuracy of dose map
Micke, Lewis and Yu, “Multi-channel film dosimetry with non-uniformity
correction”, Med. Physics 37, 2523-2534 (2011).
IMRT/SBRT QA, EBT2 Film
D(cGy)
Single field
98% SBRT patient QA
3%
with EBT2 film
3 mm (Red Channel data)
Lung CA:
2000 cGy x3
2 cm
Solid line: Film
Dotted line: TPS
IMRT, H&N Field, EBT3 Film
98%
2%
2 mm
Thcik line: TPS
Thin line: EBT3
SBRT Lung Treatment
• EBT2 film used for patient QA
• Small field size
• Require fine spatial resolution, which is
NOT achievable with diode or ion chamber
array
OAR
cGy
95%
3%
3mm
D(cGy)
Composite of
3 fields
SBRT patient QA
with EBT2 film
(Red channel data)
Lung CA:
2000 cGy x3
Solid line: Film
Dotted line: TPS
2 cm
Brain SRS QA, EBT2 Film
97%
2%
2 mm
2 cm
96%
2%
2 mm
2 cm
Solid line: iPlan, Dotted line: EBT2
Chan, International Journal of Medical Physics, Clinical
Engineering and Radiation Oncology, 2012, 1, 1-7.
VMAT QA, EBT2 Film
96%
3%
3 mm
Red channel data
Solid line: Film. Dotted line: TPS
2 cm
D(cGy)
Prostate VMAT QA, EBT2 Film
Ozawa, ESTRO 2009 and 9th AOCMP 2009
VMAT, Double Arc, EBT3 Film
Scanned Image, Portrait Orientation
Coating direction
Scanning direction
Application Film
1.7 Gy 0 Gy
Reference Films
VMAT, Double Arc, EBT3 Film
Isodose Curve comparison
96.4%
2%
2 mm
Thick line: TPS, Thin line: EBT3 Film
IMRT QA (Single Field)
EBT2 vs. TPS
Agreement
MapCHECK vs. TPS
Discrepancy
cGy
Solid line: Measurement, Dotted line: TPS
cGy
Radiochromic EBT/EBT2/EBT3 Film
• Fine spatial resolution (e.g. 0.35 mm)
• No angular dependence of film response
van Battum, Med. Phys. 2008; 35: 704-716.
Lin, Master’s thesis, Taichung, Taiwan, 2006.
• Suitable for IMRT and VMAT QA
• Immediate visualization of color change
• Drawback:
Scan film after radiation exposure and then perform
quantitative data analysis
We have come a long way in
radiation therapy.
To assure the safety and quality of treatment,
More work to be done,
Further progress to be made,
Future refinement to be achieved.
THANK YOU.