A scintillating GEM for 2D-dosimetry in radiation therapy

A GEM-based dose imaging detector with optical readout for proton radiotherapy

“…Throughout a day, relative pixel-to-pixel signal in multiple measurements remains constant within 72%. These light intensity variations may be caused by gain variations due to the GEM hole diameter and shape variations and/or non-flat GEM surface due to a nonuniform or inadequate stretching when foils are glued to the frames [23,25]. Since spatial response variations are associated with particular GEM foils in the detector, they can be corrected for by applying a pixel-by-pixel correction matrix derived from an image obtained by illuminating the whole detector working area with a uniform proton field.…”

“…Improvement in spatial resolution of such detectors is challenging: due to the lack of charge amplification, the signals from such detectors become very small with decreasing pixel size. Detectors based on gas electron multiplier (GEM) [20], used in electronic or optical readout mode, are promising candidates for a variety of dosimetry applications in charged particle beams [8,[21][22][23][24]. Systems with electronic readout would have fast response and moderate spatial resolution ( $ 1-2 mm, limited by the complexity and cost of electronics).…”

“…Soon after the introduction of GEM, this scintillation, read out by a CCD camera, has been utilized in the design of an imaging detector [27]. First results on the development of 2D dose imaging detectors with optical readout were reported in [21,23].…”

“…The light emitted by the molecules of a scintillating gas mixture excited during the electron multiplication is reflected into a CCD camera lens by a mirror. The light intensity is proportional to the number of secondary electrons [23], hence the light intensity distribution read out by the CCD camera is expected to be proportional to the two-dimensional dose distribution deposited by the primary beam in the detector's sensitive volume.…”

Characterization of a scintillating GEM detector with low energy x-rays

“…Papers reporting on scintillating GEM detectors used as an imaging device have been already published (Fraga et al 1999, 2001a, Timmer et al 2002. In two recent publications (Seravalli et al 2007, we have shown the first results of the scintillating GEM detector for 2D dosimetry in an alpha particle beam and clinical carbon ion beam, respectively.…”