EBT3 Radiochromic film response in time-dependent thermal environment and water submersion conditions: Its clinical relevance and uncertainty estimation

Aim: This study aimed to find the thermal and humidity-dependent behavior of EBT3 film. The changes in the film sensitivity as well as the dosimetric region of interest in the small-size film due to its storage and setup condition were evaluated. Material and methods: Three sets of films were kept at three different thermal storage conditions. 15 films from each set were kept at 2 degrees C, 20 degrees C, and 40 degrees C storage conditions for 24 h and 48 h pre- and post-irradiation. The humidity effect (water submersion) on the film in terms of the film's edge diffusion, and change in the optical density at the central region of the film was estimated by keeping the films underwater. Results: The mean relative film sensitivity was found 1.107 f 0.123 and 0.966 f 0.028 respectively for the films stored at 40 degrees C and 2 degrees C with respect to the sensitivity of the films that were kept at room temperature (20 degrees C) each for 48 h. The dosimetric result shows that the measured dose in the dose range (2-20 Gy) was overestimated by 7.01 % (percentage mean dose difference (MDD)) in the films stored at 40 degrees C for 48 h. In contrast, it was underestimated by -4.54 % (MDD) in the films stored at 2 degrees C for 48 h compared to those kept at an ambient room temperature of 20 degrees C (MDD = 0.24%). The water-diffusion rate at the border of the EBT3 film used in this study was 0.23 mm/h. An increment of 6.8% in the optical density at the central region of the film was observed for the unexposed control film kept underwater for 24 h. The combined standard uncertainty due to five different sources of uncertainties was 2.91%. Conclusion: The sensitivity of the EBT3 film kept at 40 degrees C is always higher (overestimate) whereas lower (underestimate) for the films kept at 2 degrees C as compared to the films at normal room temperature. The correction for the changes in the net optical density due to its storage condition (thermal effect) and the dosimetry condition of water submersion (humidity effect) must be incorporated into the current protocols of film-dosimetry if the facility cannot have temperature-controlled film storage environment and if the film immersion under water is more than 4 h.