<p>The purpose of this research was to verify experimentally the buildup region dose calculation for Pinnacle<sup>3</sup> (version 9.0), a commercial treatment planning system, commissioned and in use at the Saskatoon Cancer Center. To achieve this, buildup dose measurements using Attix parallel-plate ionization chamber and calculations by Pinnacle<sup>3</sup>, for a variety of clinical setups, were compared. The clinical setups involved 6 MV and 15 MV photon beams, open fields, enhanced dynamic wedges, physical wedges, block tray, 85, 100 and 120 cm source-to-surface distances (SSDs), and field sizes 3 x 3, 4 x 4, 5 x 5, 8 x 8, 10 x 10, 12 x 12, 15 x 15, 20 x 20, 30 x 30 cm<sup>2</sup>. The dose difference (DD) and distance-to-agreement (DTA) were used to evaluate the discrepancy between measured and calculated dose values. Significant discrepancies between measured and calculated buildup dose values were observed because the modeling in Pinnacle<sup>3</sup> is based on measurements made using a cylindrical ionization chamber. Based on the criteria of DD less than 2% or DTA less than 2 mm, 93.7% of 1,710 dose points for the 6 MV photon beam passed while for the 15 MV photon beam, 96.1% of the 2,244 dose points passed. The dose points that did not pass these criteria were mostly for open fields, block tray fields, fields with physical wedges of 15 degrees and 30 degrees and for fields with shorter source-to-surface distances. This is attributed to the high electron contamination associated with these fields. The low levels of discrepancies between measured and calculated dose values for the 15 MV beam as compared to those of the 6 MV beam need further investigations. The good agreement between measured and calculated dose values after remodeling the Electron Contamination in Pinnacle<sup>3</sup> based on Attix chamber measurements is an indication that the Electron Contamination equation in Pinnacle<sup>3</sup> may be adequate for modeling of electron contamination in the buildup dose region. The disagreement between Attix chamber and EBT 2 film measured buildup dose values was less than 3% for 89.9% of the buildup dose measurements compared. It is recommended to use a good parallel plate ionization chamber, such as the Attix chamber, for measurements in the buildup region.</p>
| Identifer | oai:union.ndltd.org:USASK/oai:usask.ca:etd-08122011-103831 |
| Date | 15 August 2011 |
| Creators | Bassey, Bassey Ekpenyong |
| Contributors | Chijin Xiao, Li Chen, Narinder Sidhu, Pat Cadman, Rob Pywell |
| Publisher | University of Saskatchewan |
| Source Sets | University of Saskatchewan Library |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://library.usask.ca/theses/available/etd-08122011-103831/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Saskatchewan or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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