SETUP DEVIATIONS IN WEDGED PAIR IRRADIATION OF PAROTID-GLAND AND TONSILLAR TUMORS, MEASURED WITH AN ELECTRONIC PORTAL IMAGING DEVICE
SETUP DEVIATIONS IN WEDGED PAIR IRRADIATION OF PAROTID-GLAND AND TONSILLAR TUMORS, MEASURED WITH AN ELECTRONIC PORTAL IMAGING DEVICE
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DOI：
10.1016/0167-8140(95)01627-s
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发表时间：
1995-11-01
影响因子：
5.7
通讯作者：
LEBESQUE, JV
中科院分区：
文献类型：
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作者：
BEL, A;KEUS, R;LEBESQUE, JV
本研究的首要目的是利用射野影像系统，对使用楔形成对斜野治疗腮腺和扁桃体肿瘤的患者的估计平移摆位偏差进行量化。第二个目的是设计一种离线摆位验证程序，必要时提高摆位精度。31名患者接受了两个适形野（前斜野和后斜野）治疗。患者使用头部固定模固定。对于最后10名患者，改进了固定模的刚性，此外，还在外耳放置带有金属标记的蜡模用于图像关联。大约每周获取一次射野影像。利用解剖结构以及在可用时利用金属标记进行图像匹配来分析摆位偏差。偏差的一致性由从两个射野测量的颅尾方向偏差之间的相关性确定。当偏差一致时，一个治疗疗程中的平移摆位偏差可以用一个三维（3D）向量来描述。利用计算机模拟设计了一种摆位验证程序。将3D摆位偏差的统计数据用作输入。输出包括所得的摆位精度和工作量（即摆位校正次数和射野影像数量）。利用解剖结构进行图像关联时，无论是旧的还是改进后的固定模，颅尾方向的偏差都没有相关性。然而，通过使用金属标记，偏差具有相关性，并且可以进行3D分析。在三个方向上平均的标准差，系统偏差和随机偏差的分布分别等于1.8毫米和1.4毫米。应用摆位验证程序，平均每位患者进行0.7次校正，有可能将大于4毫米的3D系统偏差百分比从30%降低到2%。可以得出结论，由于旋转，无法获得一致的平移摆位偏差。为了量化3D平移摆位偏差，有必要使用额外的金属标记，这些标记在两个射野的射野影像中都可见。通过使用离线摆位验证程序，摆位精度有可能进一步提高。
The first aim of this study was to quantify estimated translational setup deviations of patients treated with a wedged pair of oblique beams for parotid gland and tonsillar tumors, using portal imaging. The second aim was to design an off-line setup verification procedure, to improve the setup accuracy, if necessary. Thirty-one patients were treated with two conformal fields (anterior-oblique and posterior-oblique). The patients were immobilized with a head cast. For the last 10 patients, the rigidity of the cast was improved while, in addition, wax molds with metal markers were placed into the outer ear for image correlation. Portal images were acquired about weekly. Setup deviations were analyzed, using anatomical structures and, when available, metal markers for image matching. The consistency of the deviations was determined by the correlation between deviations in the cranio-caudal direction, as measured from both beams. When the deviations were consistent, the translational setup deviation during a treatment session could be described by a three-dimensional (3D) vector. A setup verification procedure was designed using a computer simulation. The statistics of the 3D setup deviations were used as input. The output consisted of the resulting setup accuracy and workload (i.e., the number of setup corrections and portal images). Using the anatomical structures for image correlation, the deviations in the cranio-caudal direction were not correlated, either for the old or the improved cast. However, by using the metal markers, the deviations were correlated and a 3D analysis could be performed. The standard deviations, averaged over the three directions, were equal to 1.8 and 1.4 mm for the distribution of systematic and random deviations, respectively. Application of a setup verification procedure, with 0.7 corrections on the average per patient, could potentially reduce the percentage of 3D systematic deviations larger than 4 mm from 30 to 2%. It can be concluded that it was not possible to obtain consistent translational setup deviations, due to rotations. To quantify 3D translational setup deviations, it was necessary to use additional metal markers, which were visible in the portal images of both beams. A further improvement of the setup accuracy is possible by using an off-line setup verification procedure.