Development of a Novel Radiation Dosimeter: The Stemless Plastic Scintillation Detector
Hupman, Michael Allan
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Radiation detectors are fundamental tools for the quantitative characterization of therapeutic fields of ionizing radiation. Dosimetry measurements aim to quantify the amount of energy deposited in the body (dose). Therefore, an ideal detector would respond to radiation the same way the human body does. However, the fact that most radiation detectors are not tissue equivalent poses a major challenge. Organic electronics are attractive candidates for radiation detectors due to their potential to be made flexible, configuration highly customizable, wide selection of materials, and tissue equivalence. In this thesis we investigate a novel detector (stemless plastic scintillation detector - SPSD), which couples an organic photodiode to a plastic scintillator. Plastic scintillation detectors (PSDs) offer characteristics that are ideal for the measurement of small fields (high spatial resolution, real-time measurements, tissue equivalence, etc.). However, PSDs suffer from Cerenkov radiation (created in the optical fiber) contaminating the signal and must be corrected. The SPSD detector eliminates the need for an optical fiber to carry the signal. Such a detector could have the advantages of a PSD, while removing the main drawback. A series of four manuscripts form the basis for this thesis. The first manuscript showed an organic photodiode had potential as a radiation detector directly (linearity with dose rate and output factors agreed with a commercial detector). The second explained and validated a novel method for the correction of an extraneous signal (Compton current) in organic photodiode detectors. The third manuscript investigated a single-element SPSD, which was fabricated by coupling an organic photodiode to an organic scintillator. The SPSD was characterized by measuring various dependencies of the detector including: instantaneous dose rate dependence, energy dependence, directional dependence, and linearity with dose. Furthermore, Cerenkov radiation was shown to be minimal and the directional dependence it caused could be effectively eliminated by using reflective tape. The dependencies were encouraging for use as a detector. The culmination of the work was the fourth manuscript, which presented the fabrication of a 1D array SPSD, which demonstrated the accurate measurement of small field profiles and output factors.