We describe the geometric and dosimetric characteristics of a device developed to modify the penumbra of an electron beam and thereby improve the dose uniformity in the overlap region when fields are abutted. The device is a Lipowitz metal block placed on top of the electron applicator's insertion plate and positioned to stop part of the electron beam. The air-scattered electrons beyond the block increase the penumbra width from about 1.4 to 2.7-3.4 cm. The modified penumbra is broad and almost linear at all depths for the 9 MeV and 12 MeV electron beams used in this study. Film dosimetry was used to obtain beam profiles and isodose distributions. Without the penumbra generator, lateral setup errors of 2 to 3 mm may introduce dose variations of up to 20% in the junction region. Similar setup errors cause less than 5% dose variations when the penumbra generator is used to match the fields.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.24018 |
| Date | January 1996 |
| Creators | Lachance, Bernard, 1967- |
| Contributors | Pouliot, Jean (advisor), Podgorsak, Ervin B. (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: 001529341, proquestno: MM19827, Theses scanned by UMI/ProQuest. |
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