Purpose: EBT-XD is the latest GafchromicTM film model designed to cover up to 40Gy dose level. Characterizing the temporal structure of its response to radiation is an important step toward better understanding its use and handling. The purpose of this work is to investigate the development of the response of EBT-XD and EBT3 films from several minutes up to 2 months after irradiation.
Methods: Film samples (5×5cm2 pieces) were placed between solid water phantoms and irradiated with a 6 MV beam. Two film samples for each model were irradiated in dose range 2 to 40 Gy for EBT-XD and 1 to 10 Gy for EBT3. The net optical density (OD) was measured using a flatbed scanner post-irradiation, every 5 to 10 min during the first 6 hours, every 20 to 40 min from 6-12 h, and every 24 hours for the first 5 days, and every 10 days beyond that until 2 months post-irradiation.
Results: The largest growth rate in the net OD of the film was observed during the first 3 hours after irradiation, whose variation depended on the dose delivered and color channel used for analysis (e.g. ~3.3%/h in the 15-Gy-irradiated EBT-XD film). In the time interval of 3-12 hours, the increase in the film response was much slower (~0.7%/h) From 12-24 hours, the response continues to develop at a slower pace (~0.4%/h). From 24-120 hours a small change (~0.1%/h) was noted. Beyond the 5th day, ~0.02%/h in OD was observed.
Conclusion: The polymerization of both film models was observed to be continuously developing post-irradiation manifested as an increase in the net OD. A two-exponential model could fit the net OD up to 5 days, beyond that a three-exponential model provided a better fit to the net OD.
Not Applicable / None Entered.