Effect of scanning position and orientation on the readout of Gafchromic film scanned with two different light-emitting flatbed scanners.

The present study investigates the dose readout characteristics of Gafchromic EBT3 films over a dose range of 0.5-5 Gy using two flatbed scanners in-built with different light sources, Epson Expression 11000XL and 12000XL. Film readouts were acquired repeatedly at varying scan positions and film orientations to evaluate scanner-related non-uniformities. At 0.5 Gy, the maximum variation in optical density over the entire scan frame was 15.5%, 13%, and 29%, for the red, green, and blue channels, respectively, for the Epson 11000XL, compared with 9.5%, 7%, and 22.3%, for the Epson 12000XL. At 5 Gy, the corresponding maximum differences were 2.5%, 4.0%, and 4.1%, for the 11000XL, and 6.7%, 2.5%, and 10.1%, for the 12000XL. Changes in film orientation relative to the scan direction introduced additional variability. For the Epson 11000XL, the highest orientation-related differences at 0.5 Gy and 5 Gy were 15.3%, 2.1%, and 10.4%, and, 6.3%, 3.6%, and 1.3%, for the red, green, and blue channels, respectively. In the Epson 12000XL, the corresponding differences were higher at low dose, reaching 8.2%, 7.0%, and 26.8% at 0.5 Gy, and 5.5%, 8.5%, and 4.7% at 5 Gy. The results demonstrate that scanner response is non-uniform across the scan area and is influenced by film orientation, position, irradiation dose, and scanner light source, with effects more pronounced at lower doses. LED-based scanners exhibit marginally superior performance compared with fluorescent lamp-based systems. Consistent film orientation and position during scanning is therefore recommended. A standard operating flowchart for scanner calibration and quality assurance is proposed.