Characterization of Gafchromic^TM EBT4 film with clinical kV/MV photons and MeV electrons

Objective: A newly developed Gafchromic^TM EBT4 film model was released recently. According to the vendor-stated specifications, this new model maintains major features of its more recent predecessor, EBT3, but has a great improvement in the signal-to-noise ratio (SNR). The purpose of this study was to fully characterize the EBT4 model by testing its dose response dependence on beam energy using clinical photon and electron beams and validating its improvement in SNR. Methods: In the beam energy dependence experiments, 6 MV and 15 MV photon beams, 6 MeV, 12 MeV and 20 MeV electron beams, 120 kVp and two 250 kVp x-ray beams (with different half-layer values) were selected, representing different clinical beam energies and radiation types. In the noise and SNR analyses, only the 6 MV photon beam was selected as the representative to compare between EBT4 and EBT3 models. Results: The energy dependence test results showed that there was a slight difference (<2% at most dose levels) in the dose response among the clinical MV photons and MeV electrons. However, a large deviation (>10%) in the dose response was found for the 120 kVp x-ray beam. For the two 250 kVp x-ray beams, the difference in the dose response was moderate (<5%), but not negligible. The noise and SNR results showed a reduced noise and strengthened SNR in EBT4. Conclusion: We conclude that the EBT4 film has a minimal energy dependence for MV photon and MeV electron beams but has a notable energy dependence for kilovoltage x-ray beams, and the vendor-stated features of the reduced noise and improved SNR in EBT4 are validated.