Dosimetry characteristics of GAFCHROMIC^® EBT film responding to therapeutic electron beams

For the last 50 years, high-energy electron beams have been used mainly for treatment of superficial targets. Accordingly, two-dimensional (2D) measurements are required to determine the margin between the surface and protected normal tissues in high-dose-gradient regions. As recommended by the AAPM, 2D electron beam dosimetry should be conducted primarily with films because of their high spatial resolution and because of the fact that they produce permanent records. In this work, the dosimetric characteristics of a newly developed radiochromic film, GAFCHROMIC^® EBT film were used to study treatment parameters for therapeutic electron beams. The dose-response curve was found to be weakly dependent on the electron beam energy (within ±4%). The effect of fractionation, as well as electron beam dose rate, had small influence on the calibration curve of EBT films (±2.5% and 2%, respectively). For the investigated range of depth, dose-response curves are nearly independent of the calibration depth. As for the cone size dependence, we found that it is accurate to calibrate GAFCHROMIC^® EBT films using a 10×10 cm² cone and apply this calibration to other cone sizes.