The response of the new MD-V2-55 radiochromic film exposed to ⁶⁰Co gamma rays

The response of the new radiochromic MD-V2-55 film exposed to ⁶⁰Co gamma rays has been investigated. A HP Scanjet 7650 document flatbed scanner has been used to evaluate the response. Before studying the film response, the linearity and stability of the scanner were analysed using three calibrated neutral optical filters, finding that the scanner is linear up to an optical density equal to 1 and stable over a period of more than 6 months with a variation of about ∼0.3% on the optical density for all filters. The warm-up effect of the scanner was also evaluated and a gradual increase of about 1% in the optical density was observed during the first 15 min of successive readings. Six 1 cm² pieces of film per absorbed dose were irradiated to doses ranging from 0.5 to 6500 Gy. The response of the film was evaluated at various spatial resolutions using the two scanning modes (transmission versus reflection) of the scanner. The data analysis was made by extracting all three colour channels from the film image. The results show that the spatial resolution does not have an effect on the absolute optical density, but strongly affects the relative uncertainty in the absorbed dose. A linear dependence of the optical density with absorbed dose is observed if the film is read in transmission mode, while in the reflection mode the optical density is described by a second-order polynomial function. The dose dynamic range of the dosimetry system depends significantly on the method used to evaluate the response of the film (about a factor of 3 on the maximum absorbed dose limit for the green and blue colour channels). Finally, a comparison between this new and an old dosimetry system was also made by scanning MD-55-2 in a Microtek ScanMaker E3 scanner under the same conditions as with the HP scanner. It is observed that the new film produces lower uncertainty in the measurement, which means that it is more uniform. Good agreement is obtained between the optical densities measured for both films read in different scanners. The optical density is statistically the same in the useful dose region using both digitizers, which can be attributed to the use of neutral optical filters with known optical density to calibrate the scanners. Based on these results, it is suggested to use calibrated neutral filters to standardize the systems when flat bed document scanners are used to evaluate the film response.