GEM (Gas Electron Multiplier) is a gas detector extensively used in highenergy physics with applications in medical imaging, biotechnology, material analysis, radiation therapy dosimetry, radiation detection monitoring and even astrophysics.

This CERN patented technology has more than 50 R&D and commercial licensees around the world. In 2017, CERN experts have been developing two GEM variants: i) The Optical readout GEM, which is being tailored for online dose imaging in hadron therapy and ii) the GEMpix detector, which has applications in conventional radiotherapy.