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KMID : 1164220140260020239
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Journal of Korean Society for Radiotherapeutic Technology
2014 Volume.26 No. 2 p.239 ~ p.245
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Evaluation of dose delivery accuracy due to variation in pitch and roll
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Jeong Chang-Young
Bae Sun-Myeong
Lee Dong-Hyung
Min Soon-Ki
Kang Tae-Young
Back Geum-Mun
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Abstract
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Purpose : The purpose of this study is to verify the accuracy of dose delivery according to the pitch and roll rotational setup error with 6D robotic couch in Intensity Modulated Radiation Therapy ( IMRT ) for pelvic region in patients.
Materials and Methods : Trilogy(Varian, USA) and 6D robotic couch(ProturaTM 1.4, CIVCO, USA) were used to measure and analyze the rotational setup error of 14 patients (157 setup cases) for pelvic region. The total 157 Images(CBCT 78,
Radiography 79) were used to calculate the mean value and the incidence of pitch and roll rotational setup error with Microsoft Office Excel 2007. The measured data (3 mm, 3%) at the reference angle (0˚) without couch rotation of pitch and roll direction was compared to the others at different pitch and roll angles (1˚, 1.5˚, 2˚, 2.5˚) to verify the accuracy of dose delivery by using 2D arrayionization chamber (I’mRT Matrixx, IBA Dosimetry, Germany) and MultiCube Phantom(IBA Dosimetry, Germany). Result from the data, gamma index was evaluated.
Results : The mean values of pitch and roll rotational setup error were 0.9˚ ± 0.7, 0.5˚ ± 0.6. The maximum values of them
were 2.8˚, 2.0˚. All of the minimum values were zero. The mean values of gamma pass rate at four different pitch angles ( 1˚, 1.5˚, 2˚, 2.5˚ ) were 97.75% , 96.65%, 94.38% and 90.91%. The mean values of gamma pass rate at four different roll
angles ( 1˚, 1.5˚, 2˚, 2.5˚ ) were 93.68%, 93.05%, 87.77% and 84.96%. when the same angles ( 1˚, 1.5˚, 2˚ ) of pitch and roll were applied simultaneously, The mean values of each angle were 94.90%, 92.37% and 87.88%, respectively.
Conclusion : As a result of this study, it was able to recognize that the accuracy of dose delivered is lowered gradually as pitch and roll increases. In order to increase the accuracy of delivered dose, therefore, it is recommended to perform IGRT or correct patient`s position in the pitch and roll direction, to improve the quality of treatment.
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KEYWORD
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Pitch, Roll, Gamma index
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