Program Information
Characterization of the Effect of MRI On Gafchromic Film Dosimetry
M Reyhan*, T Chen , M Zhang , Rutgers University, New Brunswick, NJ
Presentations
MO-B-BRD-6 (Monday, March 9, 2015) 10:00 AM - 12:00 PM Room: Ballroom D
Purpose: To characterize the perturbation caused by Magnetic Resonance (MR) imaging on Gafchromic film used as a radiation detector and develop a correction method
Methods: Three sets of Gafchromic EBT2 film were compared: radiation (RAD), radiation followed by MR imaging (RAD+B), and MR imaging followed by radiation (B+RAD). The T1w and T2w MR imaging was performed using a 1.5T scanner with the films in a chicken leg phantom. Doses from 0 to 800 cGy were delivered to each set by a 6MV Linac. The time interval between radiation and MR imaging was less than 10 minutes.Film calibration was generated from the red channel from the RAD for control. Microscopic imaging was performed on two pieces of film. The effect of Specific Absorption Rate (SAR) was determined by exposing another 3 sets of films to low, medium, and high SAR through a series of pulse sequences.
Results: No discernible preferential alignment was detected on the microscopic images of the irradiated film exposed to MRI. No imaging artifacts were introduced by Gafchormic film on any MR images. On average 4% dose difference was observed between B+RAD or RAD+B, and RAD with the same calibration curve. The pixel value between the B+RAD or RAD+B and RAD films were found to follow a linear relationship pixel(RAD) = 1.02*pixel(B+RAD or RAD+B). By applying this correction, the average dose error was reduced to 2%. The SAR experiment revealed a dose overestimation with increasing SAR even when the correction was applied.
Conclusion: MR imaging introduces perturbation on Gafchromic film dose measurements by 4% on average, if the film was calibrated without the presence of MRI. This perturbation can be corrected by applying a linear correction to the pixel values. The imaging protocol should be designed to avoid delivering high SAR, for in-vivo Gafchromic film MR irradiation measurements.
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