A novel method of radiochromic film dosimetry using a color scanner

A procedure that allows the improved extraction of the dose information based on the multicolor scanning of the radiochromic film is presented. The basic principle is the determination of the dose values from each color channel of the digital film image in RGB format by applying a nonlinear calibration function. The best estimate of the dose is then a weighted mean of the dose values derived from each color channel. The weighting factors are determined in such a way that the noise in the two-dimensional dose profile is at the minimum. The calculation of the weighting factors is presented; they are chosen to be proportional to the signal-to-noise ratio, Si/v(i)2, in all three color channels, i=red, green, or blue. The data reduction can be fully computerized, including the "cleaning" of the digital image from dust and scratches. It is highly reproducible, which is important for quality assurance, and easy to use. Our novel evaluation procedure combines the good response in the low dose range of the red color with the extended dose range of the blue and green color channels (response up to 10,000 Gy), making use of one single, steady evaluation function. Therefore, a smooth evaluation is possible in a wide dose range. For the interpretation of measurements with the radiochromic films the spatial inhomogeneity of the film's response to ionizing radiation is very important. Investigations on both film types, HS and MD55-2, as well as on the new EBT film have been carried out.