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Sou-Tung Chiu-Tsao, PhD Quality MediPhys LLC, Denville, NJ

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.

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Sou-Tung Chiu-Tsao, PhD Quality MediPhys LLC, Denville, NJ

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  1. Patient Specific Quality Assurance for IMRT and VMATbased 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)

  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 Webb & McQuaid, PMB 2009; 54: 4345-4360.

  7. IMRT VMAT VMAT/IMRT Prostate Established MU ~ 600 More treatment time Output rate remains fixed Fixed gantry angle for each field • Evolving rapidly • MU ~ 300 • Less treatment time • Output rate varies with angle • Rotating gantry • Single arc, Multiple arc • Partial arc, Split arc 30 5070 90 100 105 %

  8. 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

  9. Pre-Treatment QA • 2D 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

  10. Planar Dose: Gamma Index Gamma index: Distance difference: DTA criterion: ∆d Solid: TPS Dotted: EBT2 Film Dose difference: Dose diff criterion: ∆D Low, Med Phys 2003; 30: 2455-2464.

  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. Clear Polyester - 50 mm Matte Polyester - 120 m m Adhesive Layer - 25 m m Active Layer - 28 m m Active Layer - 28 m m - 175 m m Clear Polyester EBT2 and EBT3 Films Contains yellow marker dye Color: yellow to green Less sensitive to ambient light EBT2 EBT3 Matte Polyester - 120 m 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 EBT2/3 Film inCoronal 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. 0.35 mm per pixel • Use 48 bit color mode, red, green, blue channels • Use transmission mode • Disable color correction feature

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

  20. Epson 10000XL Flatbed ScannerPortrait 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

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

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

  24. Data Analysis Method • Single 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, 2523-2534 (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 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. 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

  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 96% 3 % 3 mm D(cGy) Red channel data 2 cm Solid line: Film. Dotted line: TPS

  31. Prostate VMAT QA, EBT2 Film 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 FilmIsodose 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. 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

  36. 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.

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