Sub-3mm spatial resolution from a large monolithic LaBr₃ (Ce) scintillator

Abstract

A Compton camera prototype for ion beam range monitoring via prompt (< 1 ns) gamma detection in hadron therapy is being developed and characterized at the Medical Physics Department of LMU Munich. Co photon sources were used for 2D irradiation scans (step size 0.5 mm) as prerequisite for studying the performance of the "k-Nearest-Neighbors" algorithm developed at TU Delft [2] (together with its variant "Categorical Average Pattern", CAP) and extending its applicability into the energy range beyond the original 511 keV. In this paper we present our most recent interaction position analysis in the absorbing scintillator, leading to a considerably improved value for the spatial resolution: systematic studies were performed as a function of the k-NN parameters and the PMT segmentation. A trend of improving spatial resolution with increasing photon energy was confirmed, resulting in the realization of the presently optimum spatial resolution of 2.9(1) mm @1.3 MeV, thus reaching the design specifications of the Compton camera absorber. The specification goal was reached also for a reduced PMT segmentation of 8x8 anode segments (each with 6x6 mm 2 active area), thus allowing to reduce the complexity of the signal processing while preserving the performance.

γ-Ray position reconstruction in large monolithic LaCl3(Ce) crystals with SiPM readout

“…The latter are based on a large database of measured 2D-reference patterns, which are then used in the position-reconstruction algorithm to determine the 3D-location of the main γ-ray hit. For 50×50×30 mm 3 LaBr 3 -crystals spatial resolutions of 4.5 mm fwhm at 662 keV have been reported [32] for the so-called "Categorical Average Pattern" extension of the aforementioned k-NN algorithm.…”

Machine Learning aided 3D-position reconstruction in large LaCl$_{3}$ crystals

“…For medium-size LYSO crystals of 9 cm 2 size k-nn algorithms yield rather good resolutions of around 1.1 mm fwhm [13]. However, for larger crystals of 50 × 50 mm 2 as those used in this work, the best resolutions reported for the k-nn method are of about 4.5 mm fwhm at 662 keV [16].…”

Characterization of a Compton camera setup with monolithic LaBr<inf>3</inf>(Ce) absorber and segmented GAGG scatter detectors

“…5 the position determination in the LaBr3(Ce) scintillator for one event as part of a photon source image reconstruction is exemplified. The spatial resolution of the monolithic LaBr3(Ce) scintillator at 662 keV was previously [3] determined as 4.8(1) mm, significantly improving at higher energies (2.9(1) mm at 1.3 MeV [5]). Further improvements are expected for the energy range of prompt y-rays (3-6 MeV), from the observed energy-dependent trend of the calculated spatial resolution [3,5].…”