Imaging with secondary radiation in hadron therapy beams with the 3D sensitive voxel detector

In this work we present the technique enabling visualization of the field of scattered and secondary ions generated by primary beam. The technique uses a small 3D sensitive voxel detector composed of several layers of Timepix pixel detectors. The device is placed close to the irradiated object (outside of the primary ion beam) recording the traces of all radiation coming from the sample. Detector provides the timestamp and/or deposited energy for each single particle. The shapes of traces are very typical for different particles which allows for separation of ions from other background such as electrons and gamma photons. The 3D information form the voxel detector allows for reconstruction of direction of incoming radiation. Therefore it is possible to distinguish whether particle came with the beam or it was generated or scattered later. The back projection of reconstructed directions for all registered ions can be in suitable geometry used for generation of image of distribution of scattering or fragmentation in the volume of the irradiated object. The initial experimental study to register the out coming ion radiation from testing phantom was performed at the Heidelberg Ion Beam Therapy Center (HIT) in Germany using medical carbon ion beam.