SU‐E‐T‐498: Initial Characterization of the New EBT XD Gafchromic Film

Abstract

PurposeTo assess the dosimetric accuracy of the new EBT XD (eXtended Dose) Gafchromic film and to compare the lateral scan effect between EBT XD and EBT3 film.Methods:All films were exposed in solid water using a 6 MV beam and were analyzed with FilmQA Pro software and an Epson 10000 XL scanner. Calibration was performed using films exposed to 8 known doses from 0–3000 cGy. To assess dosimetric accuracy, a 15×18 cm2 60° EDW delivered a dose range of 200–2900 cGy to 4 separate EBT XD films. Comparison to treatment planning system (TPS) predictions was made using a gamma analysis with 2%/2mm passing criteria. To assess the lateral scan effect, 21 × 21 cm2 open fields delivered doses of 1000, 2000, and 3000 cGy isocentrically to both EBT3 and EBT XD films at 10 cm depth. Films were centered and scanned such that the widest parts of the exposed film extended lateral to the center of the scanner bed in order to maximize the lateral scan effect. Ratios of measured to TPS predicted doses for EBT3 and EBT XD film were calculated at 5 cm and 8 cm lateral from the center of the scanner bed to quantitatively assess the lateral scan effect.ResultsThe average gamma passing rate for the EDW was 98.9% (range 98.7 – 99.1%). EBT XD film exhibited minimal lateral scan effect (<1%) up to 30 Gy. In contrast, EBT3 showed an under‐response of 13% and 25% at lateral positions of 5 cm and 8 cm respectively for the 30 Gy exposure.ConclusionEBT XD can accurately measure dose over a wide dynamic range. The non‐polarizing structure of its active ingredient essentially eliminates the lateral scan effect up to at least 30 Gy. EBT XD film is therefore well suited for SRS/SBRT verification measurements.