An Experimental and Theoretical Study of the Effective Length of Embedded Scintillator Materials in End-Constructed Optical Fiber Radiation Sensing Probes

Highlights: What are the main findings? A method for constructing a simpler scintillator optical fiber radiation sensing probe is described. The efficiency of coupling scintillator luminescence into the optical fiber was analyzed, yielding the optimal length value for the scintillator sensing probe. What is the implication of the main finding? To provide a base reference for sensor fabrication, thereby further enhancing the performance of fiber-optic radiation probes in terms of spatial resolution, signal-to-noise ratio, and other aspects. Optical fiber radiation sensing probes made using inorganic scintillator materials have notable advantages in achieving high spatial resolution and building sensing arrays due to their small size and excellent linearity, serving as a key tool for dose measurement in precision radiotherapy. This study establishes a theoretical model for scintillator luminescence coupling into optical fibers, and derives a fluorescence intensity calculation formula based on the fiber’s numerical aperture and fluorescence self-absorption. The light intensity response to scintillator length for different absorption coefficients is established based on numerical simulation, providing a nonlinear fitting equation, resulting in a novel “effective length of scintillator” concept. Five probes with scintillator lengths of 0.2 mm, 0.5 mm, 1.0 mm, 1.5 mm, and 2.0 mm were prepared in the laboratory using a 3:1 mass ratio mixture of UV-setting epoxy and Gd₂O₂S:Tb powder. Tests in a clinical radiation delivery setting showed good agreement between experimental data and theory, confirming optimum effective length of the scintillator as 0.62 mm. This study indicates that inorganic scintillators for end-constructed probes do need not need to be excessively long. Analyzing the effective length can reduce scintillator usage, simplify fabrication and processing, and enhance the probe’s spatial resolution without decreasing the signal-to-noise ratio, thus offering new insights for optimizing optical fiber radiation probes.