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SU‐E‐T‐101: Is EBT3 Energy Independent for Radiation‐Therapy Photon & Electron Beams?
Author(s) -
Rubinstein A,
Tailor R,
Zhao Z
Publication year - 2013
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4814536
Subject(s) - irradiation , materials science , dosimetry , electron , beam (structure) , scanner , optics , x ray , radiation , photon energy , sensitivity (control systems) , ionization chamber , photon , nuclear medicine , cathode ray , voltage , physics , ion , nuclear physics , ionization , medicine , engineering , quantum mechanics , electronic engineering
Purpose: Evaluate the new GafChromic film EBT3 for energy dependence over clinical photon and electron beams down to75kVp Methods: A single sheet of EBT3 (Lot A04041201) was cut into small pieces. Film pieces were irradiated at 6–9 known dose levels (0.4 – 12 Gy) with 9 beams: 75, 225, and 300 kVp x‐rays, Cs‐137, Co‐60, 6 and 18 MV x‐rays, and 6 and 20 MeV electrons. At each dose level, 3 pieces of film were irradiated to provide repeats. For KV x‐ray beams including Cs‐137, irradiations were performed in air with an appropriate build‐up required for Cs‐137; whereas for other beams irradiations were performed at dmax depth in water. The exposed films were read and analyzed with combination of flat‐bed scanner (Epson 10000XL) and ImageJ software (red channel). Dose‐consistency check was performed at 75 kVp by comparing film‐response curve with exposure in‐air versus that in Solid Water (depth 2.0 cm). Results: In Ortho‐voltage region, energy dependence is significant. Film sensitivity (OD) decreases with decreasing beam energy (kVp). At 75 kVp, film‐sensitivity (OD) is 16% lower than that for 6 MV beam at 6 Gy dose level. For Mega‐voltage beams including Cs‐137, film EBT3 is found to be practically energy independent within the measurement uncertainty. Dose uncertainty arising from film uniformity and film‐to‐film variation is about the same (5 ± 1.1%) as reported1 for EBT2. Conclusion: In Kilo‐Voltage region, EBT3 shows significant energy dependence showing decrease in film‐sensitivity with decreasing beam energy. However, the film is practically energy independent for Mega‐voltage Photon & Electron beams including Cs‐137. Film‐sensitivity decrease for 75 kVp is consistent with the recently reported2 >11% reduction in OD for 50 kVp beam. In light of another recent publication3, energy dependence may arise from components < 25 KeV in the beams.