Room: AAPM ePoster Library
Purpose: To evaluate the progression of polymerization of EBT-3 radiochromic films irradiated in photon and proton beams over five days post-irradiation and identifying the optimal time for dose measurement.
Methods: EBT3 films were irradiated in a solid water phantoms at 5 cm depth for photon beam and 10 cm depth for proton beam at three doses 2 Gy, 5 Gy, and 8 Gy. The films were scanned by using a desktop flatbed scanner at various time points for up to 120 hours post irradiation. The net optical density (Net OD) of the red color channel was taken as a surrogate of polymerization in the film. The slope of the Net OD vs. time curve at different time intervals was numerically determined as an indicator of polymerization as a function of time.
Results: The net optical density of the photon-irradiated radiochromic films were higher than that of proton-irradiated films at all three dose levels. The time derivative of the proton-irradiated films shows to be steeper compared to that of photon-irradiated films. The rapid drop in the slope of the proton-irradiated films between 4h and 8h suggests a higher rate of fast component of polymerization compared to photon-irradiated films. For both types of radiation, the Net OD slopes become steady at about 24 hours post-irradiation.
Conclusion: The rate of polymerization especially the fast component differs between photon-irradiated and proton-irradiated films; however, both achieve their respective steady state levels 24 hours after irradiation for EBT3 film model.