A study of four radiochromic films currently used for (2D) radiation dosimetry

We have measured the dose, D, and dose rate, D', dependences of the radiation-induced change in optical absorption of four radiochromic films currently used for (2D) dosimetry: GafChromic® types EBT3, MD-V3, HD-V2 and HD-810. We have irradiated the films using two 60Co γ-ray sources with dose rates of ~2 and ~30 Gy/min and a 200 kVp X-ray source with dose rates from ~0.2 to ~1.0 Gy/min. The 48-bit RGB image files of the films, obtained using an Epson V700 flatbed scanner, were color-channel separated and the red, green and blue pixel levels, P(D), were determined using ImageJ software. The relationship P(D)/P(0)=[1+hD/m]/[1+D/m] is found to provide a good description of the dose dependence for all four films at all dose rates. The parameter h is the "plateau level" of P(D)/P(0) approached at high doses, i.e. P(∞)/P(0). The parameter m is the “median-dose” for which P(D)/P(0)(1+h)/2 which is the half point in the dynamic range of the particular film. The best-fit values of m over the dose rate range from ~0.2 to ~25 Gy/min using the red pixels were 1.42±0.03, 11.1±0.4, 63.6±0.9 and 60.6±1.6 Gy for EBT3, MD-V3, HD-V2 and HD-810 respectively. Using the green pixels the median dose is 1.8 times larger for the first 3 films and 2.5 times larger for HD-810. The blue pixels are considered unsuitable for dosimetry because of the large value of h (>0.4) and the resulting small dynamic range.