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Patient Specific QA with GafChromic EBT3 Films for Steotactic IMRT Plans

H Jiang*, R Badkul , N Demez , K Kauweloa , H Saleh , The University of Kansas Cancer Center, Kansas City, KS


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: When treating brain tumors of irregular shape with sterotactic radiosurgery (SRS), IMRT beams might be exclusively used or combined with 3D conformal arcs to achieve conformal dose distributions. Due to the small volume of SRS targets, patient QA with 2D diode devices faces the challenge of insufficient number of diodes being irradiated. The goal of this study is to evaluate the feasibility of using GafChromic EBT3 films for SRS patient IMRT QA.

Methods: The treatment planning system for SRS was Brainlab iPlan. In some SRS cases (e.g., meningioma or AVM), several step-and-shoot IMRT beams were added to conformal arcs to improve the plan quality. IMRT beams were delivered to EBT3 films at a depth of 10 cm in solid water on a Novalis Tx linear accelerator. A series of films were also exposed to known doses for creating the dose calibration curve. The maximum dose from the irradiated SRS IMRT beams was close to 500 cGy. The calibration curve was established to cover a dose range of 0 to 700 cGy. The IMRT field films and calibration films were scanned within 12 hours from being exposed. The film scanner was Epson Expression 10000XL, and the films were scanned with 72 dpi resolution and 48-bit RGB format. The scanned images and iPlan dose files were imported into the FilmQA Pro software for analysis. The calibration curve was created using the multichannel approach with the recommended data fitting function.

Results: Comparisons between film measurement and planned doses were performed. Decent agreement between measurement and treatment plan was achieved, including high dose and high dose gradient regions.

Conclusion: Although not a preferred method for routine IMRT QA due to its complexity and time cost, EBT3 film is a reliable choice in SRS cases where small volume and high dose gradient are involved.


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