A fiber-optics, real-time dosimeter based on optically stimulated luminescence of aluminum oxide:carbon and potassium bromide:europium, for potential use in the radiotherapy of cancer.

摘要

This thesis describes a single-fiber dosimetry system based on Optically Stimulated Luminescence (OSL) of artificially grown single crystals of Al 2O3:C and KBr:Eu, with potential applications in the medical field, and especially in radio-oncology. Small fiber-shaped dosimeters having dimensions (diameter/length) on the order of 0.5 mm/5 mm are attached to one end of an optical fiber, resulting in fiber probes having diameters of less than 1 mm and lengths of up to 15 m. The opposite end of the fiber is connected to an OSL reader that contains a stimulation light source (laser) and a photomultiplier tube (PMT) used for luminescence detection.; During irradiation, an opto-mechanical shutter periodically allows the laser light to be transmitted down the optical fiber, and to stimulate the luminescence response from the dosimeter being irradiated at a remote location. The luminescence measured during each interval of laser stimulation is indicative of the radiation dose absorbed in the dosimeter since the previous stimulation. The integral absorbed dose is obtained via a summation procedure from the measured dose fractions.; Several operating procedures and data processing algorithms were developed in order to increase the speed and the accuracy of the measurements, and integrated in the software controlling the automated operation of the OSL readers. The periodic modulation of the stimulation also allows the OSL signal to be discriminated from the background fluorescence, and thus yields measurements unaffected by the Cerenkov light (the so-called "stem effect").; Depending on the type of material used, the speed of the measurements, expressed as the time required to estimate an individual dose fraction, can be as short as 67 milliseconds. Integral dose estimations from real-time OSL of Al2O3:C and KBr:Eu were obtained for water-phantom irradiations performed with medical teletherapy sources, and were found to agree within 3.7% and 2.8%, respectively, with reference measurements from ionization chambers.; We also investigated the possibility of using the fiber OSL readers for alternative purposes, such as 2-dimensional mapping of dose distributions on compacted layers of Al2O3:C grains, and detection of low-level doses, with applicability in Homeland Security projects.