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Development of an in Vivo Dosimetry System Using Radiophotoluminescence from Silver-doped Phosphate Glass for Radiotherapy Applications

Shrestha, Nishan
The goal of this project was to determine the potential of using radiophotoluminescence (RPL) from silver-doped phosphate glass as a real-time, in vivo dosimeter in radiation therapy. Our objective is to develop a portable RPL reader and identify the technical difficulties and potential solutions to decide on the feasibility of such system. Two different setups were built to characterize the material luminescence properties, such as the excitation/emission wavelength, to select proper optical filters for the system. The stimulation and detection components of the system were characterized to understand the overall stability of the system. Additional material characteristics, including the dose build up effect, were also studied. Based on these studies a qualitative model for the RPL properties was proposed. The results show that that the diode laser when operated in QCW mode is limited by the laser rise and fall time, which needs to be taken in to account when taking time discrimination measurements. There is background fluorescence in the system which reduces the sensitivity and dynamic range of the system. It was also found that the increase in temperature of the RPLGD and laser intensity reduces the RPL intensity with time. However, with use of proper neutral density filters this problem can be resolved. A model based on some of the new findings about the material has been proposed to explain build-up effect, temperature dependence, and UV bleaching effect which were not presented in literature or explained by previous models. The rate of build up was characterized and it was found to be independent of dose or dose rate. Thus, a universal build-up curve can in principle be formulated and used to calculate dose from an irradiated sample based on the readout time.