  Purpose: For more than a decade that plastic optical fiber based dosimeters
have been developed for medical applications. The feasibility of dosimeters
using optical fibers that are almost Cherenkov light free has been demonstrated
in some prototypes, particularly suitable for photon high-energy beams. In the
energy range up to a few hundred keV, where the production of Cherenkov light
by secondary electrons is negligible or small, the largest source of background
are the fluorescence mechanisms. Methods: In recent years our group has
developed an optical fiber dosimeter with photodiode readout named DosFib,
which has small energy dependence in the range below 100 keV relevant for
radiology. Photodiodes are robust photodetectors, presenting good stability
over time and enough sensitivity to allow the use of an electrometer as a
measuring device without extra electronics. Results: In-vitro tests using a
High Dose Rate 192Ir source have demonstrated its suitability for brachytherapy
applications using this important radioactive source. Attenuation curves have
been obtained in water with the DosFib dosimeter and an ionization chamber and
the depth dose profiles shown to be identical. Conclusions: This new dosimeter
can thus be calibrated and used in clinical measurements with good competitive
advantages over other dosimeters.
