WE-D-BRF-04: Experimental Investigations On Ion Radiography with Beam Scanning Using a Range Telescope

Purpose: Ion beams exhibit a finite range and an inverted depth-dose profile, the Bragg peak. These favorable properties allow superior tumordose conformality, but introduce sensitivity to range uncertainties. Hence, imaging techniques play an increasingly important role to support the treatment planning and the in-vivo monitoring of the actual ion beam treatment. Methods: This work presents the experimental investigations carried out to address the feasibility of ion transmission imaging at the Heidelberg Ion Therapy center using an active raster scanning beam delivery system and a prototype range telescope set-up based on a stack of 61 parallel-plate ionization chambers (PPIC) interleaved with 3 mm absorber plates of PMMA. Results: An extensive characterization of the set-up in terms of beam parameters and settings of the read-out electronics was performed and results will be presented. A data processing method to increase the range resolution (MIRR) of the PPIC stack was developed. In this approach, the position of the maximum of the Bragg curve is deduced from the ratio of measured signals in adjacent PPIC channels. MIRR evaluation is based on Bragg curves obtained from Monte Carlo simulations and validated with experimental data acquired with the PPIC stack using ion beams. MIRR was applied to the carbon ion radiography of an anthropomorphic Alderson head phantom yielding a resolution of 0.8 mm water equivalent thickness (WET) compared to the nominal value of 3.495 mm WET given by the thickness of the absorber slabs in the PPIC stack. An absolute comparison of the Alderson phantom carbon ion transmitted image with an X-ray digitally reconstructed radiography, both converted into WET, will also be shown. Conclusion: The obtained results are very promising and motivate further developments of the system towards an eventual clinical use.This work is supported by the German Research Foundation and the German Academic Exchange Service. This work is supported by the German Research Foundation (DFG) and the German Academic Exchange Service (DAAD).