SU‐C‐BRB‐01: Development of Dynamic Gimbaled X‐Ray Head Swing Irradiation Technique

Abstract

Purpose:The Vero4DRT has a unique gimbaled x‐ray head with rotating around orthogonal two axes. The purpose of this study was to develop a new irradiation technique using the dynamic gimbaled x‐ray head swing function.Methods:The Vero4DRT has maximum field size of 150Χ150 mm2. The expanded irradiation field (expanded‐field) for the longitudinal direction which is vertical to the MLC sliding direction, was created by the MLC motion and the gimbaled x‐ray head rotation. The gimbaled x‐ray head was rotated ± 35 mm, and the expanded‐field size was set as 150Χ220 mm2. To irradiate uniform dose distribution, the diamond‐shaped radiation field was created and continuously moved for the longitudinal direction. It was achieved by combination of opening and closing of the MLC and gimbal swing rotation. To evaluate dosimetric characteristic of the expanded‐field, films inserted in water‐equivalent phantoms at 100 mm depth were irradiated and the field size, penumbra, flatness and symmetry were analyzed.In addition, the expanded‐field irradiation technique was applied to virtual wedge irradiation. Wedged beam was acquired with the delta–shaped radiation field. 150Χ 220 mm2 fields with 15, 30, 45, and 60 degree wedge were examined. The wedge angles were measured with irradiated film and compared with assumed wedge angles.Results:The field size, penumbra, flatness and symmetry of the expanded‐field were 150.0 mm, 8.1–8.4 mm, 2.8% and −0.8% for the lateral direction and 220.1 mm, 6.3–6.4 mm, 3.2% and −0.4% for the longitudinal direction at 100 mm depth. The measured wedge angles were 15.1, 30.2, 45.2 and 60.2 degrees. The differences between assumed and measured angles were within 0.2 degrees.Conclusion:A new technique of the gimbal swing irradiation was developed. To extend applied targets, especially for whole breast irradiation, the expanded‐field and virtual wedge irradiations would be effective.