Treatment of intra-fractional moving tumours in the thorax and upper abdominal region using ion beams requires motion compensated beam delivery [1] but also reliable dose monitoring. Positron emission tomography (PET) can be applied to image the autoactivation occuring along the beam path during irradiation and it has turned out that PET delivers valuable information when evaluating the radiation induced activity in static targets. Depending on the available scanner type the PET measurement is carried out with a double-head scanner during irradiation (in-beam), immediatly afterwards with a scanner inside the treatment room (in-room) or with a conventional full-ring scanner in close vicinity to the treatment room (off-beam) [2]. Since 2008 a lot of experience was gained from time-resolved (4D) inbeam PET measurements with moving phantoms using the double-head PET scanner BASTEI at the former medical beam line at GSI [3].