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KMID : 0384620100210040340
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Korean Journal of Medical Physics
2010 Volume.21 No. 4 p.340 ~ p.347
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A Method to Calculate a Pass Rate of the γ-index Analysis in Tomotherapy Delivery Quality Assurance (DQA)
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Park Dahl
Kim Yong-Ho
Kim Won-Taek
Kim Dong-Won
Jeon Ho-Sang
Nam Ji-Ho
Lim Sang-Wook
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Abstract
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DQA, a patient specific quality assurance in tomotherapy, is usually performed using an ion chamber and a film. The result of DQA is analysed with the treatment planning system called Tomo Planning Station (TomoPS). The two-dimensional dose distribution of film measurement is compared with the dose distribution calculated by TomoPS using the γ-index analysis. In γ-index analysis, the criteria such as 3%/3 mm is used and we verify that whether the rate of number of points which pass the criteria (pass rate) is within tolerance. TomoPS does not provide any quantitative information regarding the pass rate. In this work, a method to get the pass rate of the γ-index analysis was suggested and a software PassRT which calculates the pass rate was developed. The results of patient specific QA of the intensity modulated radiation therapy measured with I’mRT MatriXX (IBA Dosimetry, Germany) and DQA of tomotherapy measured with film were used to verify the proposed method. The pass rate was calculated using PassRT and compared with the pass rate calculated by OmniPro I’mRT (IBA Dosimetry, Germany). The average difference between the two pass rates was 0.00% for the MatriXX measurement. The standard deviation and the maximum difference were 0.02% and 0.02%, respectively. For the film measurement, average difference, standard deviation and maximum difference were 0.00%, 0.02% and 0.02%, respectively. For regions of interest smaller than 24.3×16.6 cm2 the proposed method can be used to calculate the pass rate of the gamma index analysis to one decimal place and will be helpful for the more accurate DQA in tomotherapy.
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KEYWORD
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TomoTherapy, Patient specific quality assurance, γ-index
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