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 [ 18 F]FDG. Methods: Detectors with p-terphenyl thicknesses of 3 mm, 1 mm, 0.6 mm, and 0.4 mm were tested using a liquid [ 18 F]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 [ 18 F]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.