Scintillation Fiber-Optic Detectors for Dosimetry of 60 MeV Proton Beam

Scintillation fiber-optic detectors (FODs) offer a compact, electrically passive, and versatile solution for real-time proton beam monitoring in clinical radiation therapy. In this work, we systematically investigate and compare FODs based on GAGG:Ce, Al₂O₃:C, and Al₂O₃:C,Mg crystal scintillators under identical proton irradiation conditions. The detectors were evaluated using a 60 MeV clinical proton beam over a dose range of 0.5-15 Gy, with radioluminescence spectra acquired at integration times as short as 70 ms. The GAGG:Ce-based FOD exhibited the highest signal intensity, a fast temporal response, and excellent stability under repeated irradiation cycles, enabling reliable real-time dose monitoring. In contrast, the FODs based on Al₂O₃:C and Al₂O₃:C,Mg demonstrated high sensitivity, reproducible dose-response characteristics, and a low effective atomic number (Z_eff ≈ 11), providing near tissue-equivalent behavior. Mg co-doping modified the luminescence characteristics of Al₂O₃:C by enhancing the contribution of visible emission centers. However, under the present proton irradiation conditions, the overall RL signal remained lower than that of Al₂O₃:C while preserving good signal stability. All detector configurations maintained consistent performance across multiple irradiation cycles, with GAGG:Ce showing the lowest signal variation. Overall, these results demonstrate that scintillation FODs constitute a robust platform for proton beam diagnostics and dosimetry. GAGG:Ce-based detectors are shown to have promising potential for real-time proton beam monitoring, whereas sapphire-based detectors provide advantages for dosimetric applications where tissue equivalence is essential.