GEANT4-based evaluation of crystal length effects on the performance of a CsI(Tl) intraoperative gamma probe

Intraoperative gamma probes are essential tools in radioguided surgery, providing real-time localization of radiolabeled tissues. The performance of these probes is strongly influenced by detector design parameters, particularly the scintillation crystal length, which governs the balance between detection efficiency and spatial accuracy. In this study, the effect of CsI(Tl) crystal length on the performance of an intraoperative gamma probe coupled to a PIN photodiode was systematically evaluated using the GEANT4 Monte Carlo simulation framework. The geometry and material composition of a clinically used gamma probe were first reconstructed and benchmarked against manufacturer catalog data to validate the simulation model. Subsequently, simulations were performed for varying crystal lengths, and key performance metrics-including sensitivity, angular sensitivity, energy resolution, and spatial resolution were quantitatively analyzed for gamma-ray energies in the range of 140-511 keV. The results reveal that crystal length has a significant impact on probe performance, highlighting inherent trade-offs between sensitivity and spatial resolution. These findings provide design-oriented insight for the optimization of scintillation-based intraoperative gamma probes across clinically relevant energy ranges.