  An advanced Compton telescope appears to be the best instrument concept for
the next generation gamma-ray space observatory in the MeV range. A first
prototype of advanced Compton telescope is being developed to match the
constraints of a nano satellite mission, with the scientific objective of
measuring gamma-ray burst prompt emission polarization. Our instrumental
developments for this project are focusing on the position-sensitive
calorimeter module, made of a monolithic inorganic CeBr$_3$ scintillator read
by a pixelated photodetector. 3D position reconstruction is obtained by
deep-learning algorithms that have been optimized down to an uncertainty of 2
mm for each spatial direction.
