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Fiber-optic-coupled scintillation dosimeters are characterized by their small active volume if compared to other existing systems, and are therefore particularly suited for internal in vivo dosimetry. Due to possible differences between calibration conditions (i.e., room temperature) and conditions of clinical application (i.e., body temperature), their temperature dependence should be accurately studied. In this work, the temperature dependence of a Ce3+ doped SiO2 scintillation detector coupled to a SiO2 optical fibre was investigated for high dose rate brachytherapy applications. To this aim, two sets of irradiations with two different Ir-192 sources were performed in a water bath phantom at water temperatures ranging between 17°C and 40.4°C (Experiment 1). The relative response of the dosimeter was collected and analyzed. The same experiment was repeated with a second optical fibre which was designed without the active Ce3+ doped part at its end (Experiment 2) as well as by changing the length of the passive fibre inserted in water (Experiment 3). The two sets of measurements of experiment 1 were in accordance, indicating a linear increase with temperature of the scintillator sensitivity, with an average increase of 0.27 ± 0.2%/°C. In experiment 2, a 0.5%/°C increase of the collected signal resulted for the passive fibre. No significant difference of the temperature coefficient was found by changing the length of the fibre inserted in water (experiment 3). The obtained results show that a temperature-specific correction factor should be adopted at temperatures different than room temperature (e.g. for in vivo internal dosimetry). Further studies are required to understand the observations. © 2014 Elsevier Ltd. All rights reserved.

Fiber-optic-coupled scintillation dosimeters are characterized by their small active volume if compared to other existing systems. However, they potentially show a greater stem effect, especially in external beam radiotherapy where the Cerenkov effect is not negligible. In brachytherapy, due to the lower energies and the shorter high dose range of the employed sources, the impact of the stem effect to the detector accuracy might be low. In this work, the stem effect of a Ce3+ doped SiO2 scintillation detector coupled to a SiO2 optical fiber was studied for high dose rate brachytherapy applications. Measurements were performed in a water phantom at changing source-detector mutual positions. The same irradiations were performed with a passive optical fiber, which doesn't have the dosimeter at its end. The relative contribution of the passive fiber with respect to the uncorrected readings of the detector in each one of the investigated source dwell positions was evaluated. Furthermore, the dosimeter was calibrated both neglecting and correcting its response for the passive fiber readings. The obtained absolute dose measurements were then compared to the dose calculations resulting from the treatment planning system. Dosimeter uncertainties with and without taking into account the passive fiber readings were generally below 2.8% and 4.3%, respectively. However, a particular exception results when the source is positioned near to the optical fiber, where the detector underestimates the dose (-8%) or at source-detector longitudinal distances higher than 3cm. The obtained results show that the proposed dosimeter might be adopted in high dose rate prostate brachytherapy with satisfactory accuracy, without the need for any stem effect correction. However, accuracy further improves by subtraction of the noise signal produced by the passive optical fiber. © 2013 Elsevier Ltd.