The aim of this study was to investigate the dosimetric performance of a novel optical fiber sensor for use in external beam radiation therapy. Repeatability and reproducibility of the output signal, linearity, dose rate and dose per pulse dependence were evaluated. Angular dependence was investigated in the axial and azimuthal planes. The percentage depth dose and lateral dose profiles were measured using the optical fiber sensor system and compared to commercially available detectors such as Exradin W1 plastic scintillator and a PTW-microdiamond detector. The result of this study show that the optical fiber sensor system has good repeatability and reproducibility of the output signal with a maximum deviation of 0.17% and 1.00%, respectively. The system also showed an excellent linearity with dose, and its signal was independent of dose rate. However, the system showed a strong dependence on dose per pulse with 27% deviation from the W1 result at the highest dose per pulse value that was achieved at 75 cm source to surface distance. The system also showed an angular dependence when the incident beam was in the azimuthal plane due to the geometry of the scintillator at the tip of the fiber. The optical fiber sensor overresponded when measuring percentage depth dose curves and lateral dose profiles due in part to the sensitivity of the scintillating material (Gd2O2S:Tb) to low energy scattered radiation. However, further investigation is needed to quantify the overall contribution of Cerenkov radiation to the over-response of the optical fiber sensor.

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The purpose of this study was to design and evaluate the performance of four novel inorganic scintillating detectors (ISDs) on the Small Animal Radiation Research Platform (SARRP). Relative scintillator output, measurement repeatability, setup uncertainty, linearity with dose rate, and signal reproducibility over time were investigated. The Gd2O2S:Tb detector had the highest relative signal output, generating up to 219 times more charge than a previously characterized BCF-60based plastic scintillating detector (PSD). The Gd2O2S:Tb detector was then used to measure 220 kVp therapy beam profiles of 10 x 10 and 5 x 5 mm 2 fields. Beam profiles using the ZnS-based phosphor were also obtained and compared to investigate the performance of a lower density inorganic scintillator. 10 x 10 and 5 x 5 mm 2 therapy beam profile measurements made with the Gd2O2S:Tb and BCF-60 detectors differed, on average, by 1.1% and 1.9%, respectively. The ZnS:Ag measurements differed, on average, by 2.5% and 6% relative to BCF-60 measurements of the 10 x 10 and 5 x 5 mm 2 beam profiles, respectively. MicroCT imaging of the detector volumes was also performed, revealing poor packing of the ZnS:Ag crystalline phosphor in the deepest region of the cylindrical cavity. The Gd2O2S:Tb detector, in particular, has proven to be a promising candidate for real-time dosimetry of small fields in small animal irradiators, primarily because of the very large signal intensities observed, along with good repeatability, dose rate linearity, reproducibility and agreement with beam profile measurements made with a previously validated detector.