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Effect of Magnetic Field in Radiochromic Film Dosimetry

O Volotskova

O Volotskova1*, X Fang2 , M Keidar2 , H Chandarana1 , I Das1 , (1) NYU Medical Center, New York, NY, (2) The George Washington University, Washington, DC


TU-D-FS4-4 (Tuesday, August 1, 2017) 11:00 AM - 12:15 PM Room: Four Seasons 4

Purpose: To evaluate the dose response and changes in microscopic structures of the gafchromic film EBT3 exposed to a 1.5T magnetic field and exposed to standard and flattening filter-free (FFF) beams.

Methods: The gafchromic EBT3 film was cut into 5x5cm2 sheets/samples from one batch. The samples were exposed to a 1.5T B-field in an abdominal sequence for 7 min in MRI scanner before and after irradiation with 6X and 6XFFF beams. Doses of 0, 3, 6, 9, 12 and 18 Gy were delivered to the samples placed at a 5 cm depth in the solid water phantom. The sample orientation was maintained for during exposure and readout. The samples were scanned with an Epson Expression 11000XL in 48-bit RGB color mode at 300 dpi. Scanned images were processed in Image J and red channel mean intensity values were recorded. The samples were then coated with 6 nm gold and imaged by SEM Teneo (5kV, 13pA) under 2000, 2500, and 3000 magnifications.

Results: No significant changes in optical density (dose) were detected in controls and samples pre- and post-exposed to the 1.5T B-field in dose ranges between 3 to 18Gy. The film microstructure changes were dose dependent. The orientation and granular size of samples at higher doses were altered compared to controls. Needle-shaped particles of the active layer were longer and aligned for samples exposed to higher doses and magnetic field.

Conclusion: Fine structures of the gafchromic film represent the polymerization characteristics that are affected by the magnetic field thus possible radiation dose. Upon exposure to radiation, diacetylene monomers undergo polymerization that forms longer chains with a temporal response. Even though this study did not notice any changes in optical density, this should be studied in simultaneous application of the magnetic field during the treatment in MR-linac unit.

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