Effects of rotation and scanning spatial resolution on gafchromic film response in high energy photon beam

One of the main parameters which can affect the precision of the gafchromic film dosimetry results is scanning procedure of irradiated films. The effects of film scanning resolution as well as film orientation inside the flat-bed scanner on the final gafchromic film response have been evaluated in the current study. Gafchromic EBT2 films were used in the current study. The films were cut into 2 × 1 cm² and irradiated by different dose levels of 0-600 cGy using 6 MV clinical photon beam produced by an ELEKTA compact linear accelerator. To evaluate the effect of scanning spatial resolution on film response, irradiated films were scanned with different dpi values of 50, 72, 200, and 300. Accordingly, relevant signal to noise ratios (SNR) were measured. Furthermore, films were scanned at different angles of 0-, 30-, 60-, and 90-degrees respect to the scan direction and corresponding dose-response curves were acquired and compared to assess the effect of film orientation inside the scanner bed. The results showed that both parameters have a measurable impact on the film response. The SNR decreased by increasing the dpi value (e.g. SNR reduces about 50 % with changing dpi from 50 to 300). Film rotation inside the scanner bed can also considerably affect the film dose-response curve so that the film rotation from zero to 90° can change the film response by 59 % at the maximum level. Based on the results, it can be concluded that lower scanning dpi values (lower than 100) can improve the film response SNR and precision of the developed film dosimetry system. Furthermore, any film rotation during the film readout inside the scanner bed should be avoided, because it can considerably change the film response and relevant dosimetry data.