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dc.title : Validation of the daily quality assurance tool tomodiagnostics for helical tomotherapy
dc.creator : LELIE, Steven
dc.subject :
dc.description.abstract : Abstract presented for the annual symposium of the Belgian society of clinical physics in Leuven. Validation of the daily quality assurance tool TomoDiagnostics for helical tomotherapy Lelie S. (1), Van de Vondel I. (2), Tournel K. (2), Duchateau M. (2), Verellen D.(2) , Schroeyers W. (1) (1) XIOS Hogeschool Limburg (2) Radiotherapie, Oncologisch Centrum, Universitair Ziekenhuis Brussel Introduction: Due to a particular method of dose delivery helical tomotherapy introduced some new quality assurance aspects. Traditional methods cannot always be applied in this setting and the development of new schedules is necessary. Some of the factors, such as machine output, should be checked daily. Unfortunately the IMRT measurements, used to check dose output, take about 50 minutes, which is a lot of time. That's why at the UZ Brussel a method was developed that uses the MVCT-detector of the machine, as well as the dose chamber output. It compares these values to reference values and takes about 200 seconds. The aim of this study was to relate these values to the actual IMRT measurements on phantom, making it possible to reduce QA time significantly. Method and materials: Both IMRT and detector measurements were performed during a period of six weeks. The IMRT measurement consists of 4 measurements with an A1SL ionization chamber (Standard Imaging, Madison, US) on a planned tomotherapy cheese phantom (Gammex RMI, Middleton, US), which include cylindrical off and on axis targets. Secondly the detector measurement was performed and a linear regression was calculated between the 5 parameters received from the procedure and the date from the IMRT measurements. Results: After 10 datasets were fed to the regression, the model was able to predict future measurements with a precision of 0.5% (measured over model ratio). Conclusion: Using detector information, daily QA on tomotherapy can be reduced from 50 minutes to 200 seconds. Abstracts vi Abstract English Background and Purpose: Helical tomotherapy introduced, due to its particular method of dose delivery, some new quality assurance (QA) aspects because traditional methods cannot always be used in this setup. The delivered dose distribution in helical tomotherapy is highly dependent on the output and the shape of the beam ('cone profile') as the system does not use the traditional flattening filter. Small variations in these two parameters can have huge influences on IMRT-treatment making daily dose monitoring top priority, but very time consuming using conventional methods. This study represents the validation of an in-house developed tool 'TomoDiagnostics' which is a completely automatic daily QA tool which is fully automated and independent of other dosimetric tools. This method should reduce the daily QA time from 50 minutes to 5 minutes. Materials and Methods: The 'TomoDiagnostics' software package was developed to work independently on the system and to retrieve the integrated MVCT detector and dose chamber data directly without the need for pre-processing. The system will daily compare cone profile and the three system dose chambers to a fixed reference. It will also analyze these signals to calculate target and magnetron condition. To validate the link between output, cone profile and daily patient QA, a dedicated IMRT plan containing disjunctive target volumes on- and off-axis of linac rotation was used and a regression model was built to relate the TomoDiagnostics data with the ionization chamber measurements for the IMRT plan. Results: The results show that the in-house tool can be used to monitor output and cone shape for a tomotherapy unit in a fast and reliable way. Furthermore the tool has the ability to separate the effects of cone profile and output in one single measurement with two main parameters. Using a 4D linear regression the software is capable of predicting the IMRT ionization chamber measurements within 0.5%. Also the system is capable of predicting system related problems such as target failure prematurely. Conclusion: The in-house developed software tool based on detector and dose chamber monitoring can be used to monitor output and cone profile variations in one procedure. By using a regression the tool can also replace the IMRT QA measurements provided that an extensive QA ionization chamber measurement is made once a week. This allows that the weekly QA time will be reduced from 250 minutes to 70 minutes.
dc.publisher : Xios
dc.contributor :
dc.date : 2008
dc.type : Electronic Thesis or Dissertation
dc.format : application/pdf
dc.identifier : http://doksxios.pxl.be/doks/do/record/Get?dispatch=view&recordId=Sxhl8ae57e8c1ebb4538011ebb7c0d8c0007
dc.language : eng
dc.rights : All rights reserved
etd.degree.name : Industrieel ingenieur nucleaire technologie
etd.degree.level : Master
etd.degree.discipline : Medisch nucleaire technieken
etd.degree.grantor : Xios
 
 

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