Geometrical accuracy of the Novalis stereotactic radiosurgery system for trigeminal neuralgia
Geometrical accuracy of the Novalis stereotactic radiosurgery system for trigeminal neuralgia
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DOI：
10.3171/sup.2004.101.supplement3.0351
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发表时间：
2004-11-01
影响因子：
4.1
通讯作者：
Greathouse, HE
中科院分区：
文献类型：
--
作者：
Rahimian, J;Chen, JC;Greathouse, HE
对象。在立体定向放射外科治疗中，严格的几何精度和精度是必需的。当以非常高的辐射剂量（90戈瑞）对一个小靶标(如用于治疗三叉神经痛（直径3至4毫米）的一小部分进行治疗时，准确的靶向尤为重要。本研究的目的是确定每个步骤的不准确性，包括成像、融合、治疗计划和最后的治疗。作者实施了详细的质量保证方案。使用Radionics几何幻影室对Novalis立体定向系统的整体几何精度进行了评估。幻影有几个不同形状和大小的磁共振（MR）和计算机断层扫描（CT）成像友好的物体。使用t -1加权三维破坏梯度回忆脉冲序列和临床患者使用的CT扫描方案获得轴向1 mm厚的幻膜MR和CT图像。在知道幻影中物体的确切物理尺寸的情况下，测量了MR图像失真、CT扫描分辨率和图像融合不精度引起的绝对误差。采用Winston-Lutz测试测量诺瓦利斯龙门和患者支持系统的等心精度。由于误差是累积的，为了计算系统的整体空间精度，计算所有误差的均方根（RMS）。为了验证该技术的准确性，将一个直径1.5 mm的球形标记固定在放射变色膜的顶部，并与立体定向坐标系的x-z平面平行。将标记物定义为CT图像上的一个目标，用7个非共面圆弧对胶片上的目标进行处理。计算出的系统均方根值与目标的位置和放射线变色膜上的最高密度相关。图像融合和MR成像的平均空间误差分别为0.41 +/- 0.3和0.22 +/- 0.1 mm。龙门和沙发等心度分别为0.3 +/- 0.1和0.6 +/- 0.15 mm。包括和不包括沙发误差的情况下，系统的总体RMS值分别为0.9和0.6 mm（由于沙发旋转引起的等中心变化在沙发位置之间进行了微调整）。标记的位置验证在放射变色膜上最高光密度的0.7 +/- 0.1 mm范围内，与系统的总体RMS值相关良好。总体平均系统偏差为0.32±0.42 mm。空间误差最大的是图像融合和龙门旋转。为作者的立体定向放射外科项目制定了一个全面的质量保证计划，包括医学成像、直线加速器机械等向心性和治疗交付。为了成功治疗三叉神经痛，必须保证4mm锥的总体RMS值等于或小于1rum。
Object. Stringent geometrical accuracy and precision are required in the stereotactic radiosurgical treatment of patients. Accurate targeting is especially important when treating a patient in a single fraction of a very high radiation dose (90 Gy) to a small target such as that used in the treatment of trigeminal neuralgia (3 to 4-mm diameter). The purpose of this study was to determine the inaccuracies in each step of the procedure including imaging, fusion, treatment planning, and finally the treatment. The authors implemented a detailed quality-assurance program.Methods. Overall geometrical accuracy of the Novalis stereotactic system was evaluated using a Radionics Geometric Phantom Chamber. The phantom has several magnetic resonance (MR) and computerized tomography (CT) imaging-friendly objects of various shapes and sizes. Axial 1-mm-thick MR and CT images of the phantom were acquired using a T-1-weighted three-dimensional spoiled gradient recalled pulse sequence and the CT scanning protocols used clinically in patients. The absolute errors due to MR image distortion, CT scan resolution, and the image fusion inaccuracies were measured knowing the exact physical dimensions of the objects in the phantom. The isocentric accuracy of the Novalis gantry and the patient support system was measured using the Winston-Lutz test. Because inaccuracies are cumulative, to calculate the system's overall spatial accuracy, the root mean square (RMS) of all the errors was calculated. To validate the accuracy of the technique, a 1.5-mm-diameter spherical marker taped on top of a radiochromic film was fixed parallel to the x-z plane of the stereotactic coordinate system inside the phantom. The marker was defined as a target on the CT images, and seven noncoplanar circular arcs were used to treat the target on the film. The calculated system RMS value was then correlated with the position of the target and the highest density on the radiochromic film.The mean spatial errors due to image fusion and MR imaging were 0.41 +/- 0.3 and 0.22 +/- 0.1 mm, respectively. Gantry and couch isocentricities were 0.3 +/- 0.1 and 0.6 +/- 0.15 mm, respectively. The system overall RMS values were 0.9 and 0.6 mm with and without the couch errors included, respectively (isocenter variations due to couch rotation are microadjusted between couch positions). The positional verification of the marker was within 0.7 +/- 0.1 mm of the highest optical density on the radiochromic film, correlating well with the system's overall RMS value. The overall mean system deviation was 0.32 +/- 0.42 mm.Conclusions. The highest spatial errors were caused by image fusion and gantry rotation. A comprehensive quality-assurance program was developed for the authors' stereotactic radiosurgery program that includes medical imaging, linear accelerator mechanical isocentricity, and treatment delivery. For a successful treatment of trigeminal neuralgia with a 4-mm cone, the overall RMS value of equal to or less than I rum must be guaranteed.