Abstract
We have investigated Čerenkov radiation generated in phosphor-based optical fiber dosimeters irradiated with clinical electron beams. We fabricated two high-spatial resolution fiber-optic probes, with 200 and 400 μm core diameters, composed of terbium-based phosphor tips. A generalizable spectroscopic method was used to separate Čerenkov radiation from the transmitted signal by the fiber based on the assumption that the recorded signal is a linear superposition of two basis spectra: characteristic luminescence of the phosphor medium and Čerenkov radiation. We performed Monte Carlo simulations of the Čerenkov radiation generated in the fiber and found a strong dependence of the recorded Čerenkov radiation on the numerical aperture of the fiber at shallow phantom depths; however, beyond the depth of maximum dose that dependency is minimal. The simulation results agree with the experimental results for Čerenkov radiation generated in fibers. The spectroscopic technique used in this work can be used for development of high-spatial resolution fiber micro dosimeters and for optical characterization of various scintillating materials, such as phosphor nanoparticles, in ionizing radiation fields of high energy.
Highlights
Fiber-optic probes in conjunction with scintillating materials are promising candidates for radiation therapy dosimetry, such as in high-dose rate brachytherapy,[1,2] intensity-modulated radiation therapy,[3] superficial therapy,[4] and stereotactic radiosurgery.[5]
We have investigated Cerenkov radiation generated in irradiated optical fibers and found that at depths shallower than the depth of maximum dose, the intensity of the Cerenkov radiation coupled through the fiber is highly dependent on the numerical aperture of the fiber
We used a generalizable method for separation of Cerenkov radiation generated in irradiated optical fibers based on optical spectroscopy measurements
Summary
Fiber-optic probes in conjunction with scintillating materials are promising candidates for radiation therapy dosimetry, such as in high-dose rate brachytherapy,[1,2] intensity-modulated radiation therapy,[3] superficial therapy,[4] and stereotactic radiosurgery.[5]. The working principle of such a device relies on the generation of an optical signal proportional to the absorbed dose in the irradiated scintillating medium, which is collected and transmitted by the optical fiber to a detector, usually a photodiode or photomultiplier tube. The total optical signal recorded by the detector, has unwanted components in addition to the useful scintillation signal. These artifactual signals, collectively termed “stem effect,”[6,7] are composed primarily of the Cerenkov radiation generated in the irradiated portion of the fiber together with a small contribution of the intrinsic fiber fluorescence in the case of plastic fibers. Generation of Cerenkov radiation in the fiber, at angles where it is dominant, imposes a limit on the physical dimensions and spatial resolution of plastic fiber scintillators in order to achieve a reliable signal-to-background ratio
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