Room: AAPM ePoster Library
Purpose: To study the effect of magnetic field on the response of EBT-XD and EBT3 radiochromic films irradiated in MRIgRT beam.
Methods: EBT-XD and EBT3 radiochromic film samples were irradiated at various doses between 1 Gy to 20 Gy using 6 MV flattening filter free (FFF) x-rays generated by MRIdian™ MRI-guided radiotherapy system in the presence of B = 0.35 T magnetic field. Films from the same batch were irradiated at corresponding dose levels using 6 MV FFF beam from a TrueBeam™ (i.e. B = 0) linac for comparison. To study the effect of fractionation pattern on the film response, films samples were irradiated at the same dose level, but under different fractionation pattern (1, 2, and 4 fractions). The net optical density of the films was measured using a flatbed scanner. The absorbance spectra of the films were acquired using an optical spectrometer over 500-700 nm wavelength range.
Results: The net absorbance spectrum of the films, for both irradiation modalities, resulted in two absorption bands centered at 635 nm (primary) and 583 nm (secondary), characteristic of the EBT-XD (and EBT3) models. No significance difference was noted in the response (net optical density and net absorbance) of the films irradiated with and without the presence of the magnetic field. Also, no significant change in the response was noted with respect to the fractionation pattern.
Conclusion: No significant difference was observed in the response of the Gafchromic™ EBT-XD and EBT3 film models irradiated with and without the presence of a 0.35 T external magnetic field employed in a clinical MR-Linac system.