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Dose Response Curve of EBT2 and EBT3 Radiochromic Films to a Synchrotron-Produced Monochromatic X-Ray Beam

T Brown

T A D Brown1*, K R Hogstrom1,2, D Alvarez2, K Ham2, J P Dugas1,2, K L Matthews II2, (1) Mary Bird Perkins Cancer Center, Baton Rouge, LA, (2) Louisiana State University and A & M College, Baton Rouge, LA

SU-E-T-155 Sunday 3:00:00 PM - 6:00:00 PM Room: Exhibit Hall

Purpose: This work investigates the dose-response curves of Gafchromic EBT2 and EBT3 radiochromic films using synchrotron-produced monochromatic x-ray beams. These dosimeters are being utilized for dose verification in photoactivated Auger electron therapy at the LSU Center for Advanced Microstructures and Devices (CAMD) synchrotron facility.

Methods: Monochromatic beams of 25, 30 and 35 keV were generated on the tomography beamline at CAMD. Ion chamber depth-dose measurements were used to calculate the dose delivered to films irradiated simultaneously at depths from 0.7 - 8.5 cm in a 10x10x10-cm³ polymethylmethacrylate phantom. AAPM TG-61 protocol was applied to convert measured ionization into dose. Calibrations of films at 4 MV were obtained for comparison using a Clinac 21EX radiotherapy accelerator at Mary Bird Perkins Cancer Center. Films were digitized using an Epson 1680 Professional flatbed scanner and analyzed using the optical density (OD) derived from the red channel.

Results: For EBT2 film the average sensitivity (OD/dose) at 50, 100, and 200 cGy relative to that for 4-MV x-rays was 1.07, 1.20, and 1.23 for 25, 30, and 35 keV, respectively. For EBT3 film the average sensitivity was within 3 % of unity for all three monochromatic beams.

Conclusions: EBT2 film sensitivity shows strong energy dependence over an energy range of 25 keV - 4 MV. EBT3 film shows weak energy dependence, indicating that it would be the better dosimeter for Auger electron therapy.

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