An amorphous-Selenium (a-Se) based portal detector, which uses the metal substrate as a conversion plate, is studied using Monte Carlo techniques. The optimal thickness and material of the metal plate and a-Se thicknesses are investigated by modelling dose deposition in the a-Se layer for a 6 MV exit beam. Simulations of Detective Quantum Efficiency DQE(f) show that although DQE(0) increases with metal thickness up to $d sb{max},$ there is a cross-over near 1 cycle/mm which indicates that smaller metal thicknesses are more useful to visualize edges and small objects. A similar cross-over, though not as prominent, is also observed with constant metal thickness while varying a-Se thickness. Tungsten front plates are shown be optimal in terms of DQE for the plates under investigation. The effect of the scattered beam, described by the Scatter Fraction SF and Scatter-to-Primary Ratio SPR, is also modelled to ensure that the front-plate, which also acts as a scatter-rejection tool, satisfactorily filters out the scatter component. The SF is measured experimentally with a prototype imager for four metal plate/a-Se combinations and agrees with the Monte Carlo results within experimental uncertainties.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.27539 |
| Date | January 1997 |
| Creators | Lachaîne, Martin. |
| Contributors | Fallone, B. G. (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Master of Science (Department of Medical Radiation Physics.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001601811, proquestno: MQ37138, Theses scanned by UMI/ProQuest. |
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