Patient Specific Quality Assurance for IMRT and VMAT

Patient Specific Quality Assurance for IMRT and VMAT based on Radiochromic Film Dosimetry with EBT 2/EBT 3 Film Sou-Tung Chiu-Tsao, Ph. D Quality Medi. Phys LLC, Denville, NJ Presentation at the New Jersey Medical Physics Society Jun. 12, 2012

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

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

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)

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 & Mc. Quaid, PMB 2009; 54: 4345 -4360.

VMAT/IMRT Prostate IMRT VMAT 30 50 70 90 105 % • • • 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

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 • 2 D dosimetry – Ion chamber array – Diode array: Map. CHECK – Radiochromic film: EBT 2, EBT 3 film – EPID • 3 D, 4 D dosimetry – – Gel Delta 4 (2 perpendicular diode arrays ) Arc. CHECK 4 D Monte Carlo simulation

Planar Dose: Gamma Index Solid: TPS Dotted: EBT 2 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: EBT 2/3 Film Import Plan via DICOM Flatbed Scanner Results c. Gy Export via R&V System Film Expose Phantom

Film Dosimetry • Radiographic film, Kodak – XTL, XV 2, EDR 2 • Radiochromic film, Ashland (Formerly ISP) – XR-QA, XR-RV 2, EBT 3, MDV 3, HDV 2 • Fine spatial resolution • Darker shade with higher dose

EBT 2 and EBT 3 Films Contains yellow marker dye Color: yellow to green Less sensitive to ambient light EBT 2 EBT 3 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 EBT 3 Film

Common Setup for IMRT QA EDR 2 Film Measurement probe for absolute point dose EBT 2/3 Film Solid Water Film for 2 D dose distribution

EBT 2/3 Film in Phantom on Couch EBT 2/3 Film in Coronal Plane IGRT couch

EBT 2/3 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 EBT 2/EBT 3 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 10000 XL Flatbed Scanner Landscape orientation of film on the scanner bed Transparency adapter Coating direction Scanning direction 10000 XL Scanner bed

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

EBT 2/3 Film Image w/48 Bit Color Mode EBT 2/3 film RGB image consists of 3 components Separated into 3 images in red, green and blue channels

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

Absorption Spectra of EBT 2/3 Components • Active component – Signals in red and green channels • Marker dye – Signal in blue channel Courtesy: Dr. David Lewis

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).

IMRT/SBRT QA, EBT 2 Film D(c. Gy) Single field 98% SBRT patient QA 3% with EBT 2 film 3 mm (Red Channel data) Lung CA: 2000 c. Gy x 3 2 cm Solid line: Film Dotted line: TPS

IMRT, H&N Field, EBT 3 Film 98% 2% 2 mm Thcik line: TPS Thin line: EBT 3

SBRT Lung Treatment • EBT 2 film used for patient QA • Small field size • Require fine spatial resolution, which is NOT achievable with diode or ion chamber array

OAR c. Gy 95% 3% 3 mm D(c. Gy) Composite of 3 fields SBRT patient QA with EBT 2 film (Red channel data) Lung CA: 2000 c. Gy x 3 Solid line: Film Dotted line: TPS 2 cm

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

VMAT QA, EBT 2 Film 96% 3% 3 mm Red channel data Solid line: Film. Dotted line: TPS 2 cm D(c. Gy)

Prostate VMAT QA, EBT 2 Film Ozawa, ESTRO 2009 and 9 th AOCMP 2009

VMAT, Double Arc, EBT 3 Film Scanned Image, Portrait Orientation Coating direction Scanning direction Application Film 1. 7 Gy 0 Gy Reference Films

VMAT, Double Arc, EBT 3 Film Isodose Curve comparison 96. 4% 2% 2 mm Thick line: TPS, Thin line: EBT 3 Film

IMRT QA (Single Field) EBT 2 vs. TPS Agreement Map. CHECK vs. TPS Discrepancy c. Gy Solid line: Measurement, Dotted line: TPS c. Gy

Radiochromic EBT/EBT 2/EBT 3 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.