Development of expanded field irradiation technique with gimbaled x-ray head
Development of expanded field irradiation technique with gimbaled x-ray head
复制标题
万向X射线头扩大视场照射技术的开发
DOI：
10.1118/1.4895016
复制
发表时间：
2014
期刊：
影响因子：
3.8
通讯作者：
Masahiro Hiraoka
中科院分区：
文献类型：
--
作者：
Tomohiro Ono;Yuki Miyabe;Masahiro Yamada;Kenji Yokota;Shuji Kaneko;Akira Sawada;Hajime Monzen;Takashi Mizowaki;Masaki Kokubo;Masahiro Hiraoka
目的：Vero 4DRT的最大射野尺寸为150.0 × 150.0 mm。本研究的目的是使用Vero 4DRT独特的万向架X射线头开发扩展射野照射技术并评估其剂量学特性。方法：开发了两种技术。一个具有万向节摆动照射和多个静态段，包括四个单独的字段，表现出2.39°万向节旋转围绕两个正交轴。每个分段射野的中心射束轴从左右（LR）和上下（SI）方向的等中心点偏移40 mm，因此，照射野尺寸扩展至230.8 × 230.8 mm。在等中心点（中心相邻扩展射野）和距离等中心点20 mm（非相邻扩展射野）处创建相邻区域。通过调整万向节旋转和多叶准直器（MLC）的移动来建立组合分段射野的射野间隙或重叠。另一种技术的特点是动态分段照射，其中在旋转万向节的同时输送光束。通过万向节摆动运动和MLC的打开和关闭的组合来控制剂量分布。这使得作者能够在LR轴上扩展照射野，因为MLC运动的方向平行于该轴。配置220.6 × 150.0 mm的视野并进行检查。为了评价扩展射野的剂量测定特性，对插入水等效体模中50、100和150 mm深度的胶片进行辐照，并分析射野大小、半影、平坦度和对称性。此外，扩展野照射技术被应用于调强放射治疗（IMRT）。使用Vero 4DRT的扩展射野再现了使用传统直线加速器（Varian Clinac iX）创建的头颈部IMRT射野。将扩展调强放射治疗野的模拟剂量分布与实测剂量分布进行比较。在100 mm深度处，中心和非相邻扩展野的射野大小、半影、平坦度和对称性分别为230.2-232.1 mm、6.8-10.7 mm、2.3%-5.1%和−0.5%至− 0.4%。同样，在100 mm深度处，LR轴上动态段照射的射野大小、半影、平坦度和对称性分别为219.2 mm、6.0-6.2 mm、3.4%和− 0.1%。在扩展IMRT剂量分布区域，测量和模拟之间5%剂量差的通过率为85.8%，3%/3 mm γ射线通过率为96.4%。结论：使用万向架X射线头开发了扩展野照射技术。该技术有效地扩展了靶区，当考虑全乳房照射或头颈部IMRT时需要。
Purpose:The Vero4DRT has a maximum field size of 150.0 × 150.0 mm. The purpose of the present study was to develop expanded‐field irradiation techniques using the unique gimbaled x‐ray head of the Vero4DRT and to evaluate the dosimetric characteristics thereof.Methods:Two techniques were developed. One features gimbal swing irradiation and multiple static segments consisting of four separate fields exhibiting 2.39° gimbal rotation around two orthogonal axes. The central beam axis for each piecewise‐field is shifted 40 mm from the isocenters of the left–right (LR) and superior–inferior (SI) directions, and, thus, the irradiation field size is expanded to 230.8 × 230.8 mm. Adjacent regions were created at the isocenter (a center‐adjacent expandedfield) and 20 mm from the isocenter (an off‐adjacent expandedfield). The field gaps or overlaps of combined piecewise‐fields were established by adjustment of gimbal rotation and movement of the multileaf collimator (MLC). Another technique features dynamic segment irradiation in which the beam is delivered while rotating the gimbal. The dose profile is controlled by a combination of gimbal swing motion and opening and closing of the MLC. This enabled the authors to expand the irradiation field on the LR axis because the direction of MLC motion is parallel to that axis. A field 220.6 × 150.0 mm in dimensions was configured and examined. To evaluate the dosimetric characteristics of the expandedfields, films inserted into water‐equivalent phantoms at depths of 50, 100, and 150 mm were irradiated and field sizes, penumbrae, flatness, and symmetry analyzed. In addition, the expanded‐field irradiation techniques were applied to intensity‐modulated radiation therapy (IMRT). A head‐and‐neck IMRT field, created using a conventional Linac (the Varian Clinac iX), was reproduced employing an expanded‐field of the Vero4DRT. The simulated dose distribution for the expanded‐IMRT field was compared to the measured dose distribution.Results:The field sizes, penumbrae, flatness, and symmetry of the center‐ and off‐adjacent expanded‐fields were 230.2–232.1 mm, 6.8–10.7 mm, 2.3%–5.1%, and −0.5% to −0.4%, respectively, at a depth of 100 mm. Similarly, the field sizes, penumbrae, flatness, and symmetry of dynamic segment irradiation on the LR axis were 219.2 mm, 6.0–6.2 mm, 3.4%, and −0.1%, respectively, at a depth of 100 mm. In the area of expanded‐IMRT dose distribution, the passing rate of 5% dose difference was 85.8% between measurements and simulation, and the 3%/3 mm gamma passing rate was 96.4%.Conclusions:Expanded‐field irradiation techniques were developed using a gimbaled x‐ray head. The techniques effectively extend target areas, as required when whole‐breast irradiation or head‐and‐neck IMRT is contemplated.