Radioluminescence optical fibre sensors are gaining importance since these devices are promising in several applications like high energy physics, particle tracking, real-time monitoring of radiation beams, and radioactive waste. Silica optical fibres play an important role thanks to their high radiation hardness. Moreover, rare earths may be incorporated to optimise the scintillation properties (emission spectrum, decay time) according to the particular application. This makes doped silica optical fibres a very versatile tool for the detection of ionizing radiation in many contexts. Among the fields of application of optical fibre sensors, radiation therapy represents a driving force for the research and development of new devices. In this review the recent progresses in the development of rare earth doped silica fibres for dosimetry in the medical field are described. After a general description of advantages and challenges for the use of optical fibre based dosimeter during radiation therapy treatment and diagnostic irradiations, the features of the incorporation of rare earths in the silica matrix in order to prepare radioluminescent optical fibre sensors are presented and discussed. In the last part of this paper, recent results obtained by using cerium, europium, and ytterbium doped silica optical fibres in radiation therapy applications are reviewed. 1. Introduction An optical fibre based dosimeter basically consists of a small scintillator coupled to a passive fibre of suitable length for remote signal transport to an optical detector (e.g., photomultiplier, photodiode, etc.). Such configuration has several advantages in radiation dosimetry applications. Indeed, the small volume of the detector makes the radiation field perturbation negligible, leading to high spatial resolution and point dose evaluations. These systems may enable a real-time measurement of the dose, providing a direct feedback to the medical physician during a radiation therapy (RT) treatment. In vivo measurements on patients take also advantage by the lack of any electrical supply. Furthermore, provided that a suitable scintillator material is used, an optical fibre based dosimeter is characterized by high sensitivity and reproducibility, independence of sensitivity upon accumulated dose, independence of the response from the environmental conditions, linearity of the response over a wide range of doses/dose rates, high radiation hardness, and nontoxicity for medical applications. However, for an effective use of these systems as dosimeters in RT, the stem effect, that is, the
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