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Abstract

Originally designed for optical storage, fluorescent nuclear track detectors (FNTD) based on single aluminum oxide crystals contain aggregate color centers that show permanent radiochromic transformation when bombarded with ionizing radiation. Transformed centers produce high-yield fluorescence at 750 nm when stimulated at 620 nm. This enables non-destructive readout using confocal laser scanning microscopes (CLSMs). Since the intensity signal depends on the local energy deposition, 3D particle trajectories through the crystal can be assessed. Together with the excellent sensitivity of FNTDs, this enables derivation of information on track location, direction, energy loss, etc. over the entire particle and energy range found in ion beam therapy. Effects such as projectile fragmentation and secondary electron trajectories can be studied in detail with diffraction-limited resolution. Due to their biocompatibility, autoclavability and since post-irradiation chemical processing is not needed, FNTDs can show significant superiority to existing technologies such as plastic nuclear track detectors (e.g. CR-39). The Heavy Ion Therapy Research Group at the German Cancer Research Center studies FNTD technology for application on three main fields:

(a) Fundamental dosimetry quantities (w-value, I-value) in ion beams: FNTDs allow for determination of particle fluence and range with very high accuracy. (b) In vivo track-based assessment of dose to organs at risk during therapy: FNTDs represent one of a few systems that enable biological dose estimation which is the essential predictor for clinical outcome in ion beam therapy. In addition, FNTDs are small, resilient, wireless and biocompatible and can, therefore, be used within phantoms, animal models or even patients. (c) Radiobiology: Our group was the first to use FNTDs as substrate for cell ("Cell-Fit-HD"). This enables to correlate microscopic physical parameters and subcellular/cell response both in fixed and living cell and study cellular processes fundamental to ion beam radiotherapy that are hitherto little understood.

The talk will present the basic principle of FNTD technology, our group’s technical implementation as well as the latest methodological developments and application results.