SU‐GG‐T‐345: Dose Response and Energy Dependency of Gafchromic EBT2 Film over a Wide Range of Beam Energies and Modalities

Purpose: The Gafchromic films have been used generally in absolute and relative dosimetry in radiation therapy. The ISP Corporation® has recently replaced a widely used Gafchromic EBT film by a newer version, namely, “EBT2” film. The purpose of this study is to evaluate the EBT2 film for its energy dependencies and dose responses for a broad range of energies and modalities used in clinical radiation therapies. Method and Materials: The beams used for this study consisted of kilo‐voltage x‐rays (75,125, and 250 kVp), ¹³⁷Cs gamma (662 KeV), ⁶⁰Co gamma (1.17–1.33 MeV), Mega‐voltage x‐rays (6 and 18 MV), electron beams (6 and 20 MeV), and proton beams (100 and 250 MeV). The film's response was measured over the range of 0.4–10 Gy, which corresponds to optical density ranging from 0.05 to 0.74, for each of the beam energies. An X‐Rite pocket densitometer and an Epson flatbed scanner were used to read the films. Results: The measured dose response for EBT2 film over the energy ranges investigated was ±4.5% (1σ). The two extremes among the dose response data for various beams were 100‐MeV proton beams and ⁶⁰Co (or ¹³⁷Cs) beams. Uncertainty in beam calibrations was estimated to be 0.82% after compounding the margins of error from contribution of uncertainties in NIST calibration, ADCL calibration, and setup error and beam outputs. The film uniformity and film‐to‐film variation was found to be within 0.9% (1σ) for a single batch. Conclusion: Our results indicate that for measurement of relative and absolute dosimetry, EBT2 film is a robust dosimeter with weak energy dependency over a broad range of energies and modalities used in radiation therapy.