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Age and Batch Dependence of Gafchromic EBT Films in Photon and Proton Beam Dosimetry

I Das

I Das1*, Y Akino1 , (1) Indiana University- School of Medicine, Indianapolis, IN


SU-E-T-637 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose:Gafchrmoic films have undergone significant changes in characteristic over time reflected by HS, EBT, EBT2, EBT3 name. Inter- and intra- EBT film variability have been studied and found to be significant. However, age and lot/batch type have not been studied in various radiation beams that are investigated in this study.

Methods:Thirteen sets of films; 2 EBT, 6 EBT2 and 5 EBT3 films with different lot number and expiration date were acquired. Films were cut longitudinally in 3 cm width and sandwiched between two solid water slabs that were placed in a water phantom to eliminate air gap. Each set of films were irradiated longitudinally at dmax with 6 and 15 MV photon beams as well as in reference condition (16 cm range, 10 cm SOBP) in our uniform scanning proton beam. Films were scanned using an Epson flatbed scanner (ES-10000G) after 48 hours to achieve full polymerization. The profiles were compared with the depth-dose measured with ionization chamber and net optical density (net OD) were calculated.

Results:The net OD versus dose for EBT, EBT2 and EBT3 films of different age showed similar trend but with different slope. Even after calibration, differences are clearly visible in net OD in proton and photon beams. A net OD difference of nearly 0.5 is observed in photon but this was limited to 0.2-0.3 in proton beam. This relates to 20% and 15% dosimetric difference in photon and proton beam respectively over age and type of film.

Conclusion: Net OD related to dose is dependent on the age and lot of the film in both photon and proton beams. It is concluded that before any set of film is used, a calibration film should be used for a meaningful dosimetry. The expired films showed larger OD variation compared to unexpired films.

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