Temperature dependence of a Ce3+ doped SiO2 radioluminescent dosimeter for in vivo dose measurements in HDR brachytherapy

• A 0.9 mm diameter scintillation detector was recently developed for in vivo dosimetry in brachytherapy.
• Temperature dependence of the dosimeter was studied with an HDR Ir-192 brachytherapy source.
• Dosimeter sensitivity results to increase linearly with temperature.
• The average increase was of 0.27 ± 0.2% per °C in the investigated range of temperatures.

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.