Systematic characterization of new EBT4 radiochromic films in clinical x-ray beams

Objective. We aim to characterize kinetics of radiation-induced optical density in newly released EBT4radiochromicfilms exposed to clinical x-rays. Severalfilm models and batches were evaluated for thefilmsensitivity, optical signal increasing with time, relativefilm noise, and minimum detectable limits(MDL).Approach.Radiochromicfilm pieces from a single batch of EBT3 and three batches of EBT4 were exposedto doses of 77.38 cGy, 386.92 cGy, and 773.84 cGy using a 6 MV x-ray beam. Thefilms were scanned withaflatbed scanner at specific time intervals up to 120 h. The time-series net optical density of red, green andblue colors was corrected for response of the scanner with time and studied to establish the saturationcharacteristics offilm polymerization process. Dose-response from 3.86 cGy to 1935 cGy was alsodetermined for each color. MDL of thefilms was quantitatively defined as the dose that would double thenet optical density of red color above the standard deviation of the residual signal at zero dose. The relativenoise characteristics of EBT3 versus EBT4 were studied as a function of time, dose and scanner resolution.Main Results. For doses >= 100 cGy, analysis revealed a stability of optical density beyond 48 h post-exposure for EBT3 and EBT4films. EBT3films attained 80%-90% of their net optical density at 48 hwithin minutes of irradiation, compared to 72%-88% for EBT4films. The rate of growth was slowest forblue color, fastest for red, while green was in between the two. The MDL for EBT4 averaged 15 cGy forthree batches, whereas EBT3films reliably detected doses as low as 8.5 cGy.Significance. Several batches ofthe new EBT4film showed slightly lower response compared to its predecessor over 3.86 cGy to 1935 Gyrange. For all practical purposes, the post-irradiation growth of polymers ceases between 48 to 60 h forboth EBTfilms. Overall, the EBT4film exhibited noise characteristics similar to EBT3, except for lowerdoses where the noise was observed to be higher than its predecessor.