Optimization of a β probe for 18F radio-guided surgery.

BACKGROUND: Radio-Guided surgery (RGS) assists surgeons in achieving complete tumor resection through the intraoperative detection of radiation emitted by tumor-targeting radiopharmaceuticals. In recent years, direct detection of β-radiation from β-emitting radiopharmaceuticals has been investigated to overcome certain limitations of conventional γ-based RGS. In this context, a particle detector based on a lightweight scintillator (p-terphenyl) has been developed, demonstrating high β-particles efficiency and remarkable transparency to photons, motivating further optimization for applications with [18F]FDG. METHODS: Detectors with p-terphenyl thicknesses of 3 mm, 1 mm, 0.6 mm, and 0.4 mm were tested using a liquid [18F]FDG source. Measurements were performed in two experimental configurations: signal, where both positrons and annihilation photons reach the detector, and far background, dominated by isotropic annihilation photons. Signal discrimination capability was quantified using the figure of merit R=Signal/Background, and pulse amplitude spectra were analyzed to investigate threshold effects. RESULTS: Reducing the scintillator thickness resulted in a strong suppression of γ-induced background while preserving β-detection efficiency. Among the tested configurations, the 0.6 mm scintillator provided the best compromise, yielding an almost twofold improvement in signal-to-background discrimination with respect to the 3 mm reference detector. Spectral analysis confirmed that the previously adopted hardware threshold remains optimal for signal discrimination. CONCLUSIONS: A p-terphenyl scintillator thickness of 0.6 mm offers the best trade-off between β sensitivity and γ rejection for β-guided surgery applications with [18F]FDG. This study completes the experimental optimization of the β-probe for low-energy positron emitters and provides a solid basis for future in-vivo validation.