Dose imaging in radiotherapy with an Ar–CF4 filled scintillating GEM

A gaseous scintillation detector consisting of a Ar+CF4 filled GEM and a CCD camera has been investigated for the application as a position sensitive dosimeter in proton-beam radiation therapy. The light yield has been measured as a function of the CF4 concentration, operating voltage, beam intensity and beam energy. In conditions where the gas gain decreases due to a lower electric field, an increase of the amount of light per secondary electron is observed. The mixture of Ar+5% CF4 has the largest light output in absolute sense as well as per secondary electron. The scintillating Gas Electron Multiplier emits >1.5 times more light than needed and the signal-quenching in the Bragg peak which occurs in solid scintillators is reduced by a factor 4.