Development of high-Z organic scintillators for modern SPECT imaging and theranostic dosimetry

Objective: In the fight against cancer, improving the detectors performance is crucial to enhance diagnostic accuracy and optimize therapeutic monitoring. Current clinical SPECT systems predominantly rely on NaI(Tl) crystals, which, despite their advantages, suffer from limited count-rate performance due to long scintillation decay times. Our goal is to address this limitation by developing an innovative class of plastic scintillators doped with high-Z elements. These materials combine the fast timing characteristics of organic scintillators with improved gamma-ray detection efficiency via enhanced photoelectric interaction probability. Methods: Our research has focused on synthesizing novel organic fluorophores to fabricate plastic scintillators doped with high-Z elements with concentrations up to 10%. Moreover, we explored different fabrication techniques, including thermal polymerisation, photoinitiated polymerisation and resin 3D-printing. Results: The resulting prototypes show promising characteristics in terms of optical transparency, dopant homogeneity, light yield and timing performance, reaching levels comparable with commercial standards. Conclusions: These novel scintillators will be at the core of a next-generation SPECT detector, in which the doped scintillators are polymerized directly into the holes of a 3D-printed tungsten collimator, with signal readout performed by tiled CMOS sensors to fully exploit the plastics’ timing properties, and FPGA modules for data pre-processing. Moreover, they will serve for the development of a compact portable dosimeter tailored for metastatic castration-resistant prostate cancer (mCRPC) patients undergoing Lu-177-PSMA-617 radio-metabolic therapy. This device is designed to retrieve the radiopharmaceutical washout curve without requiring multiple SPECT scans, in order to customize the radiopharmaceutical prescription by determining the patient-specific radiometabolic parameters.