The use of a reflective scanner to study radiochromic film response

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Abstract
GafChromic MD-55-2 film response was studied using a flatbed, reflective Microtek ScanMaker E3 scanner, under different conditions to optimize its use. Irradiations were performed using 60Co gamma rays in a 0-300 Gy dose interval to produce a calibrated step wedge. A 24-bit colour-scale mode along with image splitting into its red, green and blue components is suggested as an improved dosimetry method over a 256 grey level (8-bit) mode, extending the dynamic range for this film. Diverse film orientation and positioning, a black or a white background, and individual step film scanning were evaluated. Unwanted normalization is overcome by adding reference black and white steps adjacent to the radiochromic film, ensuring reproducibility. The use of a red filter was found to be equivalent to the use of the red component of the image after image colour splitting. The useful range for MD-55-2 film is extended up to 300 Gy if colour components, other than red, are used to evaluate the response. Comparisons with optical density measurements show that inexpensive commercial scanners might be a good alternative to densitometers.