Abstract
The properties of a 50 mm × 50 mm × 30 mm monolithic LaBr3:Ce scintillator crystal coupled to a position-sensitive multi-anode photomultiplier (PMT, Hamamatsu H9500), representing the absorbing detector of a Compton camera under study for online ion (proton) beam range verification in hadron therapy, was evaluated in combination with either absorptive or reflective crystal surface coating. This study covered an assessment of the energy and position-dependent energy resolution, exhibiting a factor of 2.5–3.5 improvement for the reflectively wrapped crystal at 662 keV. The spatial dependency was investigated using a collimated 137Cs source, showing a steep degradation of the energy resolution at the edges and corners of the absorptively wrapped crystal. Furthermore, the time resolution was determined to be 273 ps (FWHM) and 536 ps (FWHM) with reflective and absorptive coating, respectively, using a 60Co source. In contrast, the light spread function (LSF) of the light amplitude distribution on the PMT segments improved for the absorptively wrapped detector. Both wrapping modalities showed almost no differences in the energy-dependent photopeak detection efficiency.
Highlights
Particle therapy has opened a new horizon for the treatment of tumors in the vicinity of critical organs at risk, due to the sharp dose localization in the Bragg peak
This work aims to characterize a 50 mm × 50 mm × 30 mm monolithic LaBr3:5%Ce [15] scintillator crystal, wrapped with either absorptive or reflective layer, in order to determine the optimum performance of a detector configuration to be used as an absorbing detector in a Compton camera which is presently under development for proton beam range monitoring
The dotted curves parameterize the energy dependence of the relative energy resolution according to the two-parameter function indicated in
Summary
Particle therapy has opened a new horizon for the treatment of tumors in the vicinity of critical organs at risk, due to the sharp dose localization in the Bragg peak. In order to fully exploit the beneficial properties of the well localized dose deposition in the tumor volume, a precise monitoring of the ion beam range is mandatory For this purpose, an online monitoring system based on a Compton camera designed to detect prompt (multi-MeV) γ rays, induced by nuclear reactions between the ion beam and biological tissue, is being developed at LMU Munich [7, 19]. An online monitoring system based on a Compton camera designed to detect prompt (multi-MeV) γ rays, induced by nuclear reactions between the ion beam and biological tissue, is being developed at LMU Munich [7, 19] This camera is composed of six customized double-sided Si-strip detectors (DSSSD), with an active area of a 50 mm × 50 mm, a thickness of 500 μm and segmentation of 128 strips on each side, acting as scatterer (tracker), while the absorber detector is formed by 50 mm × 50 mm× 30 mm monolithic LaBr3:Ce scintillator. This feature does contribute to increase the reconstruction efficiency of the camera (enabling the reconstruction of incompletely absorbed photon events), but it enhances the sensitivity to the source position of an incident photon from a Compton cone to an arc segment [5, 19]
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