Companding technique for high dynamic range measurements using Gafchromic films.
Van den Heuvel F., Crijns W., Defraene G.
PURPOSE: To introduce a methodology to perform dose measurements using Gafchromic films which can span several decades of dose levels. METHODS: The technique is based on a rescaling approach using different films irradiated at different dose levels. This is combined with a registration protocol correcting positioning and scaling factors for each film. The methodology is validated using TLD's for out-of-field doses. Furthermore, two examples are provided using the technique to characterize small sized radiosurgery cones and compared with measurements made with a pinpoint chamber. RESULTS: Excellent agreement with TLD, planning systems and measurement was found. The superior resolution of the film technique was apparent. CONCLUSIONS: The authors have introduced a new technique allowing users to quantify very low doses in conjunction with commissioning measurements. The use of film also provides 2D information on beam characteristics in high resolution measurements.