1. 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

2. Disclosure Statement
Consultant to Ashland Inc.
(Formerly ISP)

3. Background Safety and quality of radiation therapy
Machine equipment QA
Complex treatment modalities
Imaging devices
Immobilization/support devices
Skin dose issue

4. Complex Treatment Modalities
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)
SRS, SRT, SBRT
Stereotactic delivery of target dose
Multiple arcs
Multiple fixed gantry fields defined by stationary or dynamic MLC
Helical tomotherapy
Helical delivery of MLC fields

5. 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

6. VMAT Arc delivery of IMRT MLC leaf motion Gantry rotation
Output rate variation
VMAT: the divergent ray paths, leaf positions and segment weighting
at each gantry angle. The reconstructed parallel rays and associated
intensity-modulated beam are shown for every 4th angle. From a set
of unmodulated VMAT fields, the parallel rays are spatially modulated
Vmat by definition is an arc therapy. It utilizes an arc sweeping 360 degree. There are three mechanical axes during vmat delivery. Gantry rotation, mlc aperture shaping, and dose rate modulation. During gantry rotation, both mlc aperture and dose rate are modulated according to the designed tx plans. At certain beam angle, if the required dose is too high and can not be handled by dose rate modulation, gantry will slow down to compensate dose delivery.
Webb_PMB_2009_54_ _VMAT_considerations.pdf
Figure 4. The diagram shows the patient in the centre. Magenta dotted lines show the divergent
ray paths from a source at each of 72 gantry angles at 5◦ angular spacing. The moving source
rotates along a circle indicated by the outermost circle in the diagram. The next-in concentric
circle shows the position of the leaves at each gantry angle. Beneath the leaves (i.e., the next circle
in) the segment weighting is plotted as a grey rectangle of varying height and intensity which both
vary in proportion to the segment weighting. Beneath this (next circle in), the reconstructed bixel
maps from re-sorted parallel rays are shown with the associated parallel rays (black dotted lines).
It can be seen that these re-sorted rays have an intensity modulation.
Webb & McQuaid, PMB 2009; 54:

7. VMAT/IMRT Prostate VMAT IMRT Evolving rapidly MU ~ 300%
Evolving rapidly
MU ~ 300
Less treatment time
Output rate varies with angle
Rotating gantry
Single arc, Multiple arc
Partial arc, Split arc
Established
MU ~ 600
More treatment time
Output rate remains fixed
Fixed gantry angle for each field
So close up to the target, the dose distributions are fairly similar with vmat perhaps being slightly more conformal. Zooming out, however, we see significant differences in the dose distributions. With imrt, we see doses of 30-50% corresponding to the 5 treatment fields. However, with vmat, the 30 and 50% regions are dispersed all the way around the patient. Our ability to control the distribution of dose outside of the target is something that we are still learning how to do using the parameters available to us during optimization. Basically, though dose is delivered from all directions as the gantry moves around the patient with the multileaf collimator shape adjusting to conform to the target and block the normal tissues to the best of it’s ability.

8. Patient Specific QA Pre-treatment 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

9. Pre-Treatment QA 2D dosimetry 3D, 4D dosimetry
Ion chamber array
Diode array: MapCHECK
Radiochromic film: EBT2, EBT3 film
EPID
3D, 4D dosimetry
Gel
Delta4 (2 perpendicular diode arrays )
ArcCHECK
4D Monte Carlo simulation
Lobo_PMB_2010_55_4431_DOSXYZnrc_MC_QA_RapidArc_VMAT_TomoTherapy_cyberKnife.pdf

10. Planar Dose: Gamma Index
Solid: TPS
Dotted: EBT2 Film
Planar Dose: Gamma Index
Gamma index:
Distance difference:
Dose difference:
DTA criterion: ∆d
Dose diff criterion: ∆D
Low, Med Phys 2003; 30:

11. Pre-Treatment QA Procedure: EBT2/3 Film
Import Plan via
DICOM
Flatbed
Scanner
Results
cGy
Film
Export via
R&V System
Expose
Phantom

12. 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

13. 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
Active Layer 28
175
Matte Polyester -
120 m
Active Layer 28
Matte Polyester -
120 m
Asymmetric
Symmetric

14. Matte Polyester in EBT3 Film

15. Common Setup for IMRT QA
EDR2 Film
EBT2/3 Film
Measurement
probe for absolute
point dose
Film for 2D
dose distribution
Solid Water

16. EBT2/3 Film in Phantom on Couch
in Coronal Plane
IGRT couch

17. 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

18. 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 mm per pixel
Use 48 bit color mode, red, green, blue channels
Use transmission mode
Disable color correction feature
Drop this slide?

19. Epson 10000XL Flatbed Scanner Landscape orientation of film on the scanner bed
Transparency
adapter
Coating direction
Scanning direction
Scanner bed
10000XL
10000XL

20. Epson 10000XL Flatbed Scanner Portrait orientation of film on the scanner bed
Coating direction
Scanning direction
10000XL

21. 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
Red is highest contrast catch phrase. Blue image is RGB image--combined channels. FILMQA automatically takes from red channel

22. Absorption Spectra of EBT2/3 Film
Before exposure
After exposure of 2 Gy
636 nm
585 nm
420 nm
Courtesy: Dr. David Lewis

23. Absorption Spectra of EBT2/3 Components
Active component
Signals in red and green channels
Marker dye
Signal in blue channel
Courtesy: Dr. David Lewis

24. Data Analysis Method Single channel method Triple channel method
Red channel only
Green channel only
Blue channel only
Triple channel method
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, (2011).

25. IMRT/SBRT QA, EBT2 Film D(cGy) Single field SBRT patient QA
with EBT2 film
(Red Channel data)
Lung CA:
2000 cGy x3
Solid line: Film
Dotted line: TPS
98%
3 %
3 mm
Highest isodose line is for 200 cGy?
2 cm

26. IMRT, H&N Field, EBT3 Film 98% 2 % 2 mm Thcik line: TPS
Thin line: EBT3

27. 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

28. cGy D(cGy) 95% 3% 3mm Composite of 3 fields SBRT patient QA
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
Add spatial scale
Composite 3 fields
2000cGy/fx x 3 fx? Or
2000cGy total in 3 fx? Why is the highest isodose line is for 550 cGy?
2 cm

29. Brain SRS QA, EBT2 Film
97%
2 %
2 mm
96%
2 %
2 mm
2 cm
2 cm
Solid line: iPlan, Dotted line: EBT2
Chan, International Journal of Medical Physics, Clinical Engineering and Radiation Oncology, 2012, 1, 1-7.

30. VMAT QA, EBT2 Film Red channel data Solid line: Film. Dotted line: TPS
96%
3 %
3 mm
D(cGy)
Add spatial scale
Red channel data
2 cm
Solid line: Film. Dotted line: TPS

31. Prostate VMAT QA, EBT2 Film
Ozawa_strategy-for-VMAT-Juntendo-0843.pdf
Ozawa_9AOCMP_Eleckta_VMAT_QA_EBT_EBT2.pdf
Ozawa, ESTRO 2009 and 9th AOCMP 2009

32. VMAT, Double Arc, EBT3 Film Scanned Image, Portrait Orientation
Coating direction
Scanning direction
Application Film
1.7 Gy
0 Gy
Reference Films

33. VMAT, Double Arc, EBT3 Film Isodose Curve comparison
96.4%
2 %
2 mm
Thick line: TPS, Thin line: EBT3 Film

34. IMRT QA (Single Field) EBT2 vs. TPS MapCHECK vs. TPS Agreement
Discrepancy
cGy
cGy
Solid line: Measurement, Dotted line: TPS

35. Radiochromic EBT/EBT2/EBT3 Film
Fine spatial resolution (e.g mm)
No angular dependence of film response
van Battum, Med. Phys. 2008; 35:
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

36. Thank You. 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.