Program Information
Development of Expanded Field Irradiation Technique with Gimbaled X-Ray Head
T Ono1*, Y Miyabe2 , M Yamada3 , A Sawada4 , S Kaneko5 , H Monzen6 , T Mizowaki7 , M Kokubo8 , M Hiraoka9 , (1) Kyoto University, Kyoto, Kyoto, (2) Kyoto University, Kyoto, Kyoto, (3) Kyoto University, Kyoto, Kyoto, (4) Kyoto College of Medical Science, Kyoto, kyoto, (5) Kyoto University, Kyoto, Kyoto, (6) Kyoto University, Kyoto, Kyoto, (7) Kyoto University, Kyoto, Kyoto, (8) Institute of Biomedical Research and Innovation, Kobe, Hyogo, (9) Kyoto University, Kyoto, Kyoto
Presentations
TH-C-12A-3 Thursday 10:15AM - 12:15PM Room: 12APurpose: The Vero4DRT has a maximum field size of 150x150 mm². The purposes of this study were to develop an expanded field irradiation technique using a unique gimbaled x-ray head of Vero4DRT and to evaluate its dosimetric characteristic.
Methods: The expanded field irradiation consisted of four separate fields with 2.39 degree gimbal rotation around orthogonal two axes. The central beam axis for each field shifted 40 mm from the isocenter for longitudinal and lateral directions, and thus, the field size was expanded up to 230x230 mm². Adjacent region were created at the isocenter (center-adjacent expanded-field) and 20 mm from isocenter (off-adjacent expanded-field). To create flat dose distribution in the combined piecewise-fields, the overlapping and gaps regions on the isocenter plane were adjusted with the gimbal rotating and the MLC. To evaluate dosimetric characteristic of the expanded-field, films inserted in water-equivalent phantoms at 50, 100 and 150 mm depth were irradiated and the field size, penumbra, flatness and symmetry were analyzed.
In addition, the expanded-field irradiation technique was applied to IMRT. A head and neck IMRT field, which was planned for the conventional linac (Varian Clinac iX), was reproduced with the expanded-field of the Vero4DRT. The simulated dose distribution for the expanded IMRT field was compared to the measured dose distribution.
Results: The field size, penumbra, flatness and symmetry of center- and off- adjacent expanded-fields were 230.2-232.1 mm, 7.8-10.7 mm, 2.3-6.5% and -0.5-0.4% at 100 mm depth. The 82.1% area of the expanded IMRT dose distribution was within 5% difference between measurement and simulation, which was analyzed upper 50% dose area, and the 3%/3 mm gamma pass rate was 98.4%.
Conclusions: The expanded-field technique was developed using the gimbaled x-ray head. To extend applied targets, such as whole breast irradiations or head and neck IMRT, the expanded-field technique would be effective.
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