The electron pencil beam algorithm particular to the CadPlan treatment planning system (Varian) was evaluated for energies and field sizes spanning the clinical range. Calculated distributions were compared to measured data from an Elekta SL 25 linear accelerator. Excellent accordance was achieved between measured and calculated distributions for all energies and field sizes in cases of a uniform medium with a flat surface, perpendicular beam incidence and the standard source to surface distance (SSD) of 100 cm. CadPlan was also proficient at producing accurate distributions involving varied SSDs within the range typically employed in the clinic, 98--102 cm. However, when beam incidence was non-orthogonal to the surface, calculated distributions differed from measurement by up to 2.5 mm or 7%. The most severe discrepancies were observed for larger gantry angles. Calculated percent depth dose (PDD) curves in cases of simple slab heterogeneities were found to deviate from measured curves by at most 1.5 mm. Discontinuities appeared in all CadPlan-predicted curves, worsening in instances of non-standard conditions. Many errors stemming from such discontinuity problems could be eliminated by interpolating between values of fitting parameters tabulated in CadPlan and by offering more pencil beam and calculation grid sizes. As CadPlan has no means of accounting for scattered radiation specific to the jaws and applicator, it is unable to predict output factors with any accuracy.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.80289 |
| Date | January 2004 |
| Creators | Hodefi, Deborah |
| Contributors | Blais, Noel (advisor), Podgorsak, Ervin (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: 002032072, proquestno: AAIMQ98658, Theses scanned by UMI/ProQuest. |
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