A Scintillating GEM Detector for 2D Dose Imaging in Hadron Therapy focuses on a specialized manner for radiotherapy treatment. In radiotherapy, benefit for the patient can be achieved only if the treatment delivered to the patient is realized as planned. In particular, conformal treatments always bear the risk that an uncertainty in the delivered dose distribution may lead to an under dosage of the tumor, and/or over dosage outside the target volume. Therefore, it is mandatory to employ a quality assurance program that covers all steps of the treatment. This includes dosimetric verification of planned dose distributions, usually performed in water equivalent phantoms. This book discusses the phenomenon of hadrontherapy, where one of the problems of currently used two- or three-dimensional dosimeters for pre-treatment verification of those distributions is the energy dependence of their response in high LET radiation beams. The response of these detectors decreases for low particle energies due to saturation. This discussion results in an explanation of an operation principle of a scintillating gas detector based on GEMs and of the light emission. The scintillating GEM detector appears to be a suitable device for verifying dose distributions especially in high LET beams, in which the currently position sensitive detectors present the problem of saturation. However, the light and electric output anomaly found in a proton beam has to be studied again.