Thin cathode glass gas electron multiplier detector for carbon beam dose imaging

An optically read-out glass gas electron multiplier (G-GEM) detector is expected to simplify complicated quality assurance measurements for hadron therapies by imaging the dose distribution of the incident beam. However, the effect of secondary particles from the detector itself has not been well studied. In this paper, we evaluate a design that reduces the secondary particles from the cathode of a G-GEM detector. Specifically, we assembled detectors with thin cathodes and assessed their effect on the secondary particle production in simulations and experiments. The experiments were carried out under 290 MeV/u 12 C ion bombardment at the Heavy Ion Medical Accelerator in Chiba. The clinical intensity of the thin cathode detector was compared with that of a conventional thick cathode G-GEM detector. The improved chamber design reduced the dose contributions of secondary particles from the cathode without degrading the dose imaging performance.