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Improving the Energy Dependence of GAFChromic Dosimetry Films at Low Energies

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H Bekerat

H Bekerat1*, S Khushdeep1, D Lewis2, A Sarfehnia1, J Seuntjens1, S Devic1, (1) McGill University, Montreal, QC, (3) Ashland Specialty Ingredients , Wayne, NJ

TH-E-BRB-1 Thursday 1:00:00 PM - 2:50:00 PM Room: Ballroom B

Purpose:
Several studies have investigated the energy dependence of GAFChromic dosimetry films and shown a 5% to 10% energy dependence for energies below 100 keV. The purpose of this work is to improve the energy dependence of GAFChromic films and develop a new prototype with more uniform energy response at low energies (less than 100keV)

Methods:
The energy dependence of three commercial GAFChromic films, EBT-1, EBT-2 and EBT-3, has been investigated by irradiating the films to 2 Gy (Dose to water) at different beam qualities (50 kVp to 60Co). Also, the extrinsic energy dependence of the films is investigated using DOSRZnrc user-code of the EGSnrcMP Monte Carlo Package, by determining ratio of dose to water to dose to the active volume of the film using beam spectra calculated from SpekCalc. This software generates a nominal x-ray spectrum based on input information on experimental HVL, tube potential and added filtration data.
The investigation of the extrinsic energy response combined with experimental evaluation of the overall energy dependence of the film response should help us understand the physics behind the energy variation of the film response and help us in improving the energy dependence at low energies.

Results:
Current EBT film models show strong intrinsic energy dependence at low energies indicating low polymerization efficiency of the films active layer, which can be compensated for by boosting the dose to the active layer at those energies by the incorporation of moderate atomic number elements such as K, Cl, Al and Na into the active layer of the film and the careful adjustment of the mass percent of these elements and the configuration of the film.

Conclusions:
Improving the energy dependence is possible by careful adjustment of the composition and mass percent of the elements incorporated into the film active layer and film configuration.

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