Fifty-sixth annual meeting of the American association of physicists in medicine
SU-E-T-76: Comparing Homogeneity Between Gafchromic Film EBT2 and EBT3
We found out that homogeneity of EBT2 was different among lot numbers in previous study. Variation in local homogeneity of EBT3 among several lot numbers has not been reported. In this study, we investigated film homogeneity of Gafcrhomic EBT3 films compared with EBT2 films.
All sheets from five lots were cut into 12 pieces to investigate film homogeneity, and were irradiated at 0.5, 2, and 3 Gy. To investigate intra- and inter-sheet uniformity, five sheets from five lots were exposed to 2 Gy: intra-sheet uniformity was evaluated by the coefficient of variation of homogeneity for all pieces of a single sheet, and inter-sheet uniformity was evaluated by the coefficient of variation of homogeneity among the same piece numbers in the five sheets. To investigate the difference of ADC value in various doses, a single sheet from each of five lots was irradiated at 0.5 Gy and 3 Gy in addition to 2 Gy. A scan resolution of 72 dots per inch (dpi) and color depth of 48-bit RGB were used. Films were analyzed by the inhouse software; Average of ADC value in center ROI and profile X and Y axis were measured.
Results and Conclusion:
Intra-sheet uniformity of non-irradiated EBT2 films were ranged from 0.1% to 0.4%, however that of irradiated EBT2 films were ranged from 0.2% to 1.5%. On the other hand, intra-sheet uniformity of irradiated and non-irradiated EBT3 films were from 0.2% to 0.6%. Inter-sheet uniformity of all films were less than 0.5%. It was interesting point that homogeneity of EBT3 between no-irradiated and irradiated films were similar value, whereas EBT2 had dose dependence of homogeneity in ADC value evaluation. These results suggested that EBT3 homogeneity was corrected by this feature.