Electron arc therapy is a special radiotherapeutic technique using a rotational electron beam in the treatment of large superficial tumours following curved surfaces. In those cases, arc therapy offers the best way to optimize dose uniformity while sparing healthy tissues and critical organs. The use of this technique overcomes under or over dosage problems caused by field junctions. However, electron arc therapy presents important challenges in terms of dosimetry and treatment planning. / Clinical implementation of electron arc therapy requires the study of many parameters of influence such as the radius of curvature of the treated surface, the width of the treatment field, the total angle of irradiation and the beam energy. Monitor unit calculation to deliver prescribed dose is a very critical topic and, in general, requires acquisition of a large amount of measured dosimetric data. / This project concerns the clinical implementation of electron arc therapy using an Elekta SL-25 linear accelerator in the radiation oncology department of the Maisonneuve-Rosemont Hospital (Montreal, Canada). Firstly, the objective of the study is to observe the influence of the radius of curvature, the total arc angle and the field width on the following dosimetric parameters: depth of maximum dose, isodose distributions and electron arc beam output at the depth of maximum dose. Secondly, for our particular setup, the goal is to develop a simple monitor unit calculation method, based on an analytical model fitted through measured dosimetric data covering a large range of possible clinical situations. / In order to achieve these goals, electron arc irradiations were performed on cylindrical acrylic phantoms of different radii, successively varying the total arc angle and the field width at isocentre. Results obtained with thermoluminescent dosimeters show a minor impact of the radius of curvature variation on the percent depth dose curves. However, they show a significant impact on the beam output. It was also observed that the total arc angle influences the dose at the depth of maximum dose only up to a limit angle value, different for each radius of curvature. Finally, the field width at isocentre has an impact on the beam output as well as on the bremsstrahlung contribution at the isocentre. / Concerning the monitor unit calculation, a seven parameter analytical model fitted through measured data was obtained using Origin 7 software. A relationship giving the beam output as a function of the radius of curvature and the total arc angle was found. The field width was not included in the model, but will be part of further investigation before clinical implementation. As future work, dosimetric measurements with other energies should be carried on, mainly to be able to cover a wider range of clinical cases.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.97944 |
| Date | January 2006 |
| Creators | Duchesne, Caroline. |
| 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 | © Caroline Duchesne, 2006 |
| Relation | alephsysno: 002331429, proquestno: AAIMR24659, Theses scanned by UMI/ProQuest. |
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