Use of Gafchromic® EBT films in heavy ion therapy

Properties of a new type of radiochromic film-Gafchromic EBT-were investigated with respect to its use in heavy ion therapy. For this purpose not only radiation imaging, but also quantitative dosimetry is desirable. Improvements with respect to older types of Gafchromic films as well as an excellent spatial resolution make it to a promising candidate to be used in scanned medical ion beams. First, the influence of several effects and parameters on the net optical density measured using a commercial flatbed scanner was analyzed. Here the scanner resolution, the light scattering effect, the longtime development of the film and multiple evaluations of the film were investigated. Methods to reduce the influence of the largest sources of distortions were proposed. In carbon ion beams, the signal was observed to be equal or lower than in photon beams at the same dose, depending on the linear energy transfer. This behavior, known also for other dosimetric media, is caused by a local (microscopic) saturation which occurs around highly ionizing ion tracks. However, the overall darkening of the film was found not to saturate in the region of clinically used doses and beyond. (c) 2008 Elsevier B.V. All rights reserved.