Item – Thèses Canada

Numéro d'OCLC
Wang, Hui,1964-
Development of a portal imager and of tools for radiation treatment verification.
Ph. D. -- McGill University, 1996
Ottawa :National Library of Canada = Bibliothèque nationale du Canada,1997.
3 microfiches.
Includes bibliographical references.
A prototype electrostatic imager has been developed for megavoltage portal imaging in radiation therapy. The imager utilizes amorphous selenium (a-Se) with a front metal plate as the imager receptor and a high resolution voltmeter probe for image readout. Imaging characteristics of a-Se have been investigated theoretically through Monte Carlo simulations, and experimentally by measuring radiation discharging curves and phantom tests. The results of this study have shown that the prototype imager has high sensitivity, good spatial resolution and low noise level. Our study also reveals the potential of electrostatic imaging with metal/a-Se in megavoltage imaging. Two computer algorithms have also been developed for automatic segmentation and contrast-enhancement of digital portal images, and for radiation field shape verification. Based on a priori knowledge of the properties of portal images, the segmentation and contrast-enhancement algorithm employs multiple criteria and dynamic reasoning to achieve optimal segmentations of individual images, and has been proved to be accurate, robust and fast. The algorithm for radiation field shape verification is an adaptation of the chamfer matching technique to a specific application: matching closed contours. By incorporating geometric features of the radiation field and using a simple minimization method which is more specific to this task, the algorithm appears to be able to improve the matching results of the standard method.