Characterization and optimization of EBT2 radiochromic films dosimetry system for precise measurements of output factors in small fields used in radiotherapy

The accurate determination of absorbed dose in small photon beams, especially for stereotactic radiation therapy, is a difficult task with commercially available detectors. As these small fields are characterized by high dose gradients, a lack of lateral particle equilibrium and a variation of energy spectra with beam sizes, a dosimeter with high resolution, tissue-equivalence and high precision is required. The new radiochromic film EBT2, which meets these criteria, was fully characterized in Institut de Radioprotection et Surete Nucleaire (IRSN) for this application. This type of film was tested with the reading system EPSON Dual Lens Perfection V700 flatbed scanner in transmission mode. Warm-up effects of the scanner were studied as well as the influence of the scanner light. Uniformity of unirradiated and irradiated EBT2 films in terms of pixel value was found to be respectively 0.3% (1 SD) and 0.5% (1 SD). An original, accurate and efficient radiochromic film dosimetry protocol was established. The overall uncertainty for dose measurement with EBT2 films using this protocol was estimated at less than 2% (1 SD). Encouraging measurements of output factors were performed on a Novalis system. (c) 2011 Elsevier Ltd. All rights reserved.