Evaluation of a lead-loaded plastic scintillator for next-generation positron emission tomography detectors using Geant4 simulation.

Abstract

Purpose: Lead-loaded plastic scintillators are promising candidates for next-generation positron emission tomography (PET) detectors owing to their short fluorescence decay times, high machinability and low production cost. However, their γ-ray detection performance has not been fully quantified. This study evaluated the detection efficiency and energy-resolution characteristics of a 5 wt% lead-loaded plastic scintillator (EJ-256) and compared its performance with that of a conventional polyvinyltoluene (PVT) scintillator.

Methods: Monte Carlo simulations were performed using Geant4. Monoenergetic 511 keV gamma rays (100 000 events) were irradiated onto scintillator blocks with thicknesses varied from 20 mm to 200 mm in 5 mm increments. The resulting absorbed-energy spectra were analysed using ROOT to determine detection efficiency and the simulated full width at half maximum (FWHM) of the 511-keV photopeak. To identify the thickness region at which detection efficiency saturated, a non-parametric Kruskal-Wallis test was conducted to consecutive thickness groups to determine the point beyond which differences were no longer statistically significant (p > 0.05).

Results: EJ-256 exhibited a distinct 511 keV photopeak, whereas PVT showed only a broad Compton continuum. The detection efficiency increased from 0.9% at 20 mm to 2.9% at 200 mm and saturated above approximately 135 mm, consistent with the Kruskal-Wallis analysis. The simulated 511-keV photopeak width remained stable at approximately 10% FWHM across all thicknesses.

Conclusion: These results indicate that EJ-256 demonstrates photon-absorption performance comparable to that of conventional inorganic PET scintillators, while offering substantially faster temporal response and reduced fabrication cost. This combination suggests strong potential for application in future time-of-flight PET detector modules.