(Saturday, 4/7/2018) 10:30 AM - 12:30 PM
Room: Marquis Ballroom 5-8
Purpose: To characterize the effects on gafchromic film to MR exposure time within the 0.35T magnet on the world’s first MRIdian ViewRay linear accelerator.
Methods: Perturbations of EBT3 and XD gafchromic film due to exposure time within the magnetic field were evaluated by placing the film at isocenter of the MRIdian for 12 hours prior to irradiation, after irradiation, or without any MR exposure. Films were setup at isocenter using 7.5-cm of solid water for build-up and 7.5-cm of solid water for backscatter. A treatment plan consisting of nine different dose levels was delivered to each film, and polynomial fitting was performed to generate calibration curves. The orientation of the polymers was visualized using scanning electron microscopy (SEM). SEM images were acquired for unexposed film, films irradiated with MR exposure prior and after irradiation, and gafchromic films without any MR exposure. The orientation of the crystal polymers determines dose response. The dosimetric impact of film orientation was evaluated by films exposed to MR for 12 hours prior to irradiation in both coronal and sagittal orientations.
Results: Effect of MR exposure on derived calibration curves for either film type was negligible. Correlation of calibration curves with and without exposure was >0.99. SEM images did not show a change in crystal orientation, consistent with calibration curve results. No differences were observed due to film orientation.
Conclusion: The added effects of a 0.35T magnetic field were minimal for EBT3 and XD gafchromic film, based on comparison between film dosimetry with and without MR. These results were confirmed by experiments using scanning electron microscopy.
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