The thesis work contains two related projects. The first project examines the characteristics of the Farmer-type ionization chamber (Farmer-type IC 2571 A) used in our experiments. An investigation was carried out to determine if the simplified "two-voltage technique" used in clinics is sufficiently accurate for saturation current estimation. Three models were used to fit the measured currents and to estimate the saturation current. The estimation was carried out by measuring the currents set-up in the Farmer-type IC while varying the applied voltages, for both polarities, for fixed and variable dose rates. The second project investigated peripheral dose in 6 MV beam using the Farmer-type IC. The signal produced in the ionization chamber when measuring the peripheral dose is 2 to 3 orders of magnitude lower than the signal produced with the chamber in the primary beam, thus, the leakage and saturation characteristics of the ionization chamber had to be investigated to ensure that they do not have adverse effects on the chamber reading. Measurements were acquired in open field (10x10 cm2) and in a dynamic MLC field (10x1 cm2), with the IC at the machine's isocenter. / Measurements allowed us to determine peripheral dose due to scatter and leakage radiation. Measurements were repeated for a blocked beam, which allow us to determine only the leakage radiation component of the peripheral dose. The two components of the peripheral dose depend strongly on the linac head configuration and shielding. Leakage radiation per MU for a dMLC field is similar or higher than the leakage radiation for a static field, which implies an increase in peripheral dose for IMRT-type treatments. Knowledge of peripheral dose can be useful in estimating dose and risk to sensitive structures outside of the primary treatment field.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.97921 |
| Date | January 2006 |
| Creators | Ceusan, Florin. |
| 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 | © Florin Ceusan, 2006 |
| Relation | alephsysno: 002331237, proquestno: AAIMR24631, Theses scanned by UMI/ProQuest. |
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