Energy and dose dependence of GafChromic EBT3-V3 film across a wide energy range

Abstract

The purpose of this work is to determine the energy and dose dependence of GafChromic EBT3-V3 film over an energy range 0.2 mm Al HVL to 6 MV. Films have been irradiated at increasing dose with three different beams: 6MV beam, TPR(10,20) = 0.684 ± 0.01; HVL = 2.00 ± 0.01 mm Al and HVL = 0.20 ± 0.01 mm Al, a very-low-energy beam. The dose output for each beam was determined with an appropriate calibrated ionization chamber, following IPEM and DIN6809-4 standard recommendations. Calibration curves were generated using the same dose range (0 cGy to 850 cGy) for the three energies. Using the 6MV calibration curve as reference, the film response in terms of net optical density was evaluated. The difference in the calibration curve obtained by irradiating the film with 6MV and 2mmAl HVL energy beams is less than 3%, within the calibration uncertainty, in the dose range 400–850cGy. The maximum difference is 4.1% at 150cGy. The optical density of EBT3-V3 film is significantly lower at 0.2 mmAl HVL compared to 6MV, showing differences up to 25%, with a minimum of 16% at 850 cGy. Conclusion: when the EBT3-V3 film is irradiated at doses higher than 400 cGy, the calibration curve for the 2 mmAl beam agrees with the reference beam (6MV) within 3%. A significant under-response (by up to 25%) was seen at 0.2mmAL HVL. EBT3-V3 films are suitable dose detectors when the dose response curve is measured within the range 6MV and 2 mm Al HVL. 6MV calibration curve could be used within this range, with 3% uncertainty.