  Fluorescent nuclear track detectors (FNTDs) based on Al2O3:C,Mg single
crystal combined with confocal microscopy provide 3D information on ion tracks
with a resolution only limited by light diffraction. FNTDs are also ideal
substrates to be coated with cells to engineer cell-fluorescent ion track
hybrid detectors. This radiobiological tool enables a novel platform linking
cell responses to physical dose deposition on a sub-cellular level in proton
and heavy ion therapies. To achieve spatial correlation between single ion hits
in the cell coating and its biological response the ion traversals have to be
reconstructed in 3D using the depth information gained by the FNTD read-out.
FNTDs were coated with a confluent human lung adenocarcinoma epithelial cell
layer. Carbon ion irradiation of the hybrid detector was performed
perpendicular and angular to the detector surface. In-situ imaging of the
fluorescently labeled cell layer and the FNTD was performed in a sequential
read-out. Making use of the trajectory information provided by the FNTD the
accuracy of 3D track reconstruction of single particles traversing the hybrid
detector was studied. The accuracy is strongly influenced by the irradiation
angle and therefore by complexity of the FNTD signal. Perpendicular irradiation
results in highest accuracy with error of smaller than 0.10{\deg}. The ability
of FNTD technology to provide accurate 3D ion track reconstruction makes it a
powerful tool for radiobiological investigations in clinical ion beams, either
being used as a substrate to be coated with living tissue or being implanted in
vivo.
