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Practical Guidance for Using
Radiochromic Film
What is Radiochromic Film?
A film that instantly changes color on
exposure to ionizing radiation and needs
no chemical or physical processing
David F. Lewis
Advanced Materials Group
International Specialty Products
August 4, 2011
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Why Choose Radiochromic Film?
What are My Choices?
Film Types for Dose Measurement
• Need to measure and/or locate a radiation field
• Primarily for radiotherapy (MV photons/electrons/protons)
• No chemical processing!!!
• EBT2 - 1 cGy to >40 Gy
• High spatial resolution – down to 10 micron scale
• MD-55-V2 – 2 Gy to 100 Gy
• Wide dynamic dose range - >1000:1
• Cut to size
• Bend to conform to curved surfaces
• Water immersion
• HD-810 - 10 Gy to 400 Gy
• Primarily for radiology (kV photons)
• XR-RV3 - 5 cGy to 15 Gy
• XRQA2 – 1 mGy to 20 cGy
When asking for input on uses for radiochromic film (RCF) several sent examples of EBT2 use
between 60Gy and 100Gy. Transparent films (EBT2, MD-55-V2 and HD-810) are preferred for
dose measurement where a high degree of accuracy (better than 2%) is needed. Because of
front surface reflection from the reflective films (RTQA, XR-RV3, XRQA) their dynamic range and
accuracy is not as good (better than 5%).
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Quantitative Dose Measurement
What are My Choices?
Film Types for Beam Location
• Primarily for radiotherapy (MV photons, electrons, protons)
• RTQA2 - 2 cGy to 8 Gy
• Primarily for radiology (kV photons)
• XRQA2 - 1 mGy to 20 cGy
• XRCT2 - 1 mGy to 20 cGy
• XRM2 - 1 mGy to 20 cGy
With acknowledgements to Slobodan and Nada Devic, Samuel Trichter, Eduardo Villarreal, Jeffrey Guild, Gary Arbique and Scott Sample
The XR films contain some high Z components to boost absorbance of kV photons.
Just to illustrate the wide range of applications
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Radiochromic Film Applications - QA
Radiochromic Film Applications
• Radiotherapy dosimetry
– MV photons, electrons, protons, heavy ions
• All conformal modalities, radiosurgery
• Brachytherapy – HDR, LDR, plaques and special applicators
– kV range – photons, electrons
• Skin treatments
W ith acknowledgements to: Slobodan Devic, Theo van Soest, Andre Wopereis and Zheng Lu
Just to illustrate the wide range of applications
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Radiochromic Film Applications
Radiochromic Film Applications
• Radiotherapy quality assurance
–
–
–
–
–
–
Radiation field flatness and symmetry
Radiation and light field conformance
Iso-center - star shots
Winston-Lutz test
MLC motion and leakage
Commissioning
• Diagnostic dosimetry and quality assurance
• Interventional procedures
• Skin dose
•
•
•
•
• Replace ion chamber in the water tank????
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CT dosimetry
Mammography
Conventional diagnostic x-ray
Nuclear medicine
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GAFChromic® Dosimetry Film Configuration
Radiochromic Film Structure – HD-810
Polyester Laminate
Active Layer
Adhesive Layer
Active Layer
Tr ansparent Polyester Base
Polyester Base
Dose range: 10 to 400 Gy
• Protection
from mechanical damage and water immersion
•Transparent base: EBT2, MD-55V2
•White, opaque base: RTQA, XR-RV3, XRQA, XR-CT, XR-M
•Clear laminate: EBT2
•Yellow laminate: RTQA, XR-RV3, XRQA, XR-CT, XR-M
This is a “generic” configuration to help emphasize the first bulleted point. If you need details
some are at www.gafchromic.com, www.filmqapro.com or contact me at dlewis@ispcorp.com
Structures with “bare” active layer indispensible for:
• Skin dose measurement
• Low energy electrons, betas, alphas, protons, etc.
• Need this structure, but need high sensitivity?
•Contact me – dlewis@ispcorp.com
•
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How do I Measure Radiochromic Film?
What Essentials do I Need to Know?
• How much exposure?
• Color reference chart
– Radiotherapy films – 1 cGy to 50 Gy
– Radiology films – 1 mGy to 10 Gy
• Densitometer
• Limit exposure to light and don’t expose to UV
• Don’t expose to high temperature >60 C
• Keep track of the orientation
• Scanner
– Preferably an rgb color scanner
– 16 bit/channel resolution essential for dose measurement
• Especially important if film is cut
• Epson flatbed scanners:
• Keep track of the time after exposure
– 10000XL with transparency adapter – A3 format 12.2” x 17.2”
• Important for absolute dosimetry
– V700, V750 and 4990 – 8” x 10”
• Develop a protocol and stick to it
The basics. If you’re not using the film keep it in the dark.
Problem with Vidar scanners is that there is only one color channel and multi-channel
dosimetry is not possible. The Vidar red scanner is superior to the older white light scanners. I
have found with Microtek and other large format scanners is that I am not confident that I can
turn off the image adjustment features that give you beautiful pictures but destroy your
dosimetry. Canon and HP scanners are generally not large enough format.
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What Do I Need to Know about Scanning?
Disable all the Image Adjustment Features
• Qualitative applications
– Little more than pressing the “Scan” button
• Quantitative applications
– Disable image adjustment options in scan software
– Be consistent with the orientation of the films
• Mark films if you cut them
– Be consistent with the “time-after-exposure”
– Use the middle of the scanner
Check
“No Color Correction”
The points highlighted in yellow are common areas for mistakes from beginners.
Forget absolute dosimetry if you don’t do this, but you’ll have a pretty picture
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GAFChromic EBT2 Orientation Dependence
GAFChromic EBT2 Orientation Dependence
300
35000
Red Channel
Blue Channel
Landscape orientation
Portrait orientation
250
Scanner response
30000
150
100
50
Portrait
0.1
0.1
0.2
0.2
Density
0.3
0.3
0.4
Landscape
15000
0
30
60
90
120
Rotation Angle
150
180
Response error is ~0.05% per degree
Dose error ~0.15% per degree
0
0.0
25000
20000
Scan direction
Scan direction
Dose, cGy
200
0.4
5 misalignment
Conclusion: Misalignment unlikely to cause notable error
• Choose one orientation and stick with it
Keep track of orientation if you cut film to smaller pieces. Cut rectangular pieces and mark one
corner to disrupt the symmetry and make it obvious which way to place them.
Don’t worry. Our sense of order and tidiness make it obvious that the film placement should be
adjusted if is misaligned – unless we cut film in circles!
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Post-exposure Changes – Time After Exposure
GAFCHROMIC EBT2
0.5Gy
0.6
Optical density
1Gy
0.5
1.5Gy
0.4
2.5Gy
Dealing with Post-exposure Changes
Time after Exposure, min.
Response change, %/min.
15
30
60
120
480
0.040%
0.023%
0.011%
0.006%
0.001%
• Relative Dosimetry
0.3
• Proportional changes in dose response
• Post-exposure timing can be ignored
0.2
• Absolute Dosimetry
0.1
• Scan all films the same “time after exposure”
0.0
0.0
0.5
1.0
1.5
2.0
2.5
Log10(time, minutes)
3.0
3.5
Establish a protocol and stick with it
Maybe read a set of calibration films at different times after exposure if you want to have some
flexibility. If you’re methodical and disciplined here’s no reason why you couldn’t scan films 15
minutes after exposure. But a few hours lapsed time makes for forgiveness and overnight for a
lot of foregiveness.
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Scanner Response: Lateral Dependence Artifact
Film Placement on the Scanner
Normalized Response
Menegotti et al. 2008 Med. Phys., 35, 3078-84
Scan direction
Left side
Center
Right side
Central placement
Lateral Position
Lateral placement
Keep to the center of the scanner. That’s the message. And the “sweet spot” in the center of the
large format Epson scanner (10000XL) is bigger than the in the V700 and other 8” x10”
scanners. For my taste the extra cost of the 10000XL is well worth it for working with fields
>10cm wide.
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Why is EBT2 Film Yellow?
Single Channel Dosimetry – Lateral displacement
• Because it contains a yellow dye – a marker dye
• But why?
2.00
1.80
– To permit correction of film non-uniformities
– Red channel – dominated by active component - dose information
– Blue channel – dominated by marker dye - uniformity information
1.60
1.20
Active Component after Exposure
1.00
1.2
0.80
1.0
0.60
0.8
Marker Dye before and after Exposure
3
Before exposure
0.40
0.20
0.00
After exposure to 50Gy
2
Absorbance
Absorbance
Dose, Gy
1.40
0.6
0.4
1
0.2
0
50
100
150
200
Position, x 0.353 mm
250
300
350
0.0
400
450
500
550
Wavelength, nm
600
650
700 0
350
400
450
500
550
Wavelength, nm
600
650
700
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Single Channel Film Dosimetry
A Better Way: Triple Channel Dosimetry
• Calibration Curve X=R
Rave = Rave(D) ↔ D=D(Rave)
• Uses all the color channels
• Xave average film response
• Any X value delivers dose D(X)
• “Multi-channel film dosimetry with non-uniformity
correction”, Micke et al., Med. Phys., 38(5), p2523, 2011.
• X + ∆X → D(X) + ∆D (X=RGB)
• Any color disturbance ∆R leads to
deviation ∆D in Dose D, e.g. film
thickness variation, scanner nonlinearity
• Separates dose response from dose-independent artifacts
• Compensates for film thickness variations
• Improves dose map accuracy
• Attenuates the lateral response artifact
• Allows ‘sensing’ of calibration errors
• FilmQA Pro software – www.filmqapro.com
D=DX
Every disturbance has a dose consequence.
The marker dye is an internal reference. It’s relatively easy to get out the big non-uniformities,
but as you get better the improvements are harder and harder. Dose measurements require the
highest levels of accuracy and the marker dye and triple channel dosimetry are the way to go if
you can’t support $100 million investment in coating equipment.
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Triple Channel Film Dosimetry
• RGB Calibration Curves
• Dose induced color C
C(D) = {R(D),G(D),B(D)}
• Dose exposure generates
only ‘certain’ colors C
• Not all C deliver dose value
• Observed color Cscan
is superposed with disturbance ∆C
• Cscan = C(D) + ∆C
• Solution: Optimize dose D value, i.e. minimize ∆C
•
| Cscan - C(D) | → min ?
Triple Channel Film Dosimetry
• Definition:
Color channels in terms of ‘optical density’ d X
– dX = -log( X ) for X = R, G, B (generally wave length)
• Model:
Scanned density d X,scan is a product of two factors
– dX,scan( D ) = dX,D( D ) * ∆d
– dX,D is calibration function
– ∆d is a disturbance independent of dose + X (wave length)
e.g. ∆thickness, scanner artifact, noise, fingerprint, etc. )
• Solution:
– ∆dX = dX,scan (D) / dX,D (D) for all X = R,G,B
– Optimized dose D:
( ∆dR - ∆dB )2 + ( ∆dB - ∆dG )2 + ( ∆dG - ∆dR )2 → min
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Triple Channel Dosimetry:
Triple Channel Film Dosimetry Example
Attenuation of Lateral Placement Artifact
2.0
1.8
1.6
Dose, Gy
1.4
D RGB+ ∆ d
1.2
1.0
0.8
Red channel dosimetry
0.6
Triple channel dosimetry
0.4
0.2
0.0
0
Dose Map, Disturbance (uniformity) ∆d Map and Horizontal Profiles
50
100
150
200
250
300
350
Position, x 0.353 mm
Look at that – all the non-uniformities in the film (and this is a bad film that wouldn’t meet our
release standards) are extracted into the disturbance map. Yes!
And a very nice bonus to address the lateral placement artifact. There are some other tools built
into the FilmQAPro software that can be used for calibrating our the lateral response artifact.
But alas there’s not enough time today to dive into it. Contact me at dlewis@ispcorp.com or
Andre and amicke@ispcorp.com if you’d like to know more.
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Radiochromic Film and New Therapy Modalities
Small Field Dosimetry – High Spatial Resolution
• Trends in conformal therapy
– Less fractions
– Higher doses per fraction
– Higher dose gradients and tighter conformity
• New tendencies increase the value of:
– High spatial resolution
– High dynamic range
• Positive news for radiochromic film dosimetry
With acknowledgements to: Steve Sorensen, Stefan van Hoof, Mark Oldham, Frank Verhagen, Guillaume Landry, Shane White and Sha Chang
High spatial resolution – radiochromic film delivers!
These are all small fields on EBT2 film. 5cm, 2.5 cm fields and the one on the lower right from
Sha Chang has images of beams only ¼ mm wide. The false-color dose map from EBT2 film on
the upper right shows doses up to 58Gy on a 2 cm film. How else would you do the dosimetry?