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Temporal Variation of the Polymerization in X-Ray- and Proton-Irradiated Radiochromic Films

S Momin, A Darafsheh, R Khan*, Washington University School of Medicine, St. Louis, MO

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

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.

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Keywords

Radiochromic Film, Dosimetry, Protons

Taxonomy

TH- External Beam- Particle/high LET therapy: Proton therapy – experimental dosimetry

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