Gayou Olivier, Miften Moyed
Department of Radiation Oncology, Allegheny General Hospital, Pittsburgh, Pennsylvania 15212, USA.
Med Phys. 2007 Aug;34(8):3183-92. doi: 10.1118/1.2752374.
The improvement in conformal radiotherapy techniques with steep dose gradients has allowed for the delivery of higher doses to a tumor volume while maintaining the sparing of surrounding normal tissue. In this situation, verification of patient setup and evaluation of internal organ motion just prior to radiation delivery is a crucial step. To this end, several volumetric image-guided techniques have been developed for patient localization, such as the Siemens MVision mega-voltage cone beam CT (MV-CBCT) system. In this work, the commissioning and clinical implementation of the MVision system is presented. The geometry and gain calibration procedures for the system are described, and guidelines for quality assurance procedures are provided. Different MV-CBCT clinical protocols, ranging from daily to weekly image-guidance, which includes image acquisition, reconstruction, registration with planning CT, and treatment couch offsets corrections, were commissioned. The image quality characteristics of the MVision system were measured and assessed qualitatively and quantitatively, including the image noise and uniformity, low-contrast resolution, and spatial resolution. Furthermore, the image reconstruction and registration software was evaluated. Data show that a 2 cm large object with 1% electron density contrast can be detected with the MVision system with 10 cGy at isocenter and that the registration software is accurate within 2 mm in the anterior-posterior, left-right, and superior-inferior directions.
随着剂量梯度陡峭的适形放射治疗技术的改进，在保护周围正常组织的同时，可以向肿瘤体积输送更高的剂量。在这种情况下，放疗前患者摆位的验证和内部器官运动的评估是关键步骤。为此，已经开发了几种用于患者定位的容积图像引导技术，例如西门子MVision兆伏级锥形束CT（MV-CBCT）系统。在这项工作中，介绍了MVision系统的调试和临床应用。描述了该系统的几何和增益校准程序，并提供了质量保证程序指南。调试了不同的MV-CBCT临床方案，从每日到每周的图像引导，包括图像采集、重建、与计划CT配准以及治疗床偏移校正。对MVision系统的图像质量特征进行了定性和定量测量与评估，包括图像噪声和均匀性、低对比度分辨率以及空间分辨率。此外，对图像重建和配准软件进行了评估。数据表明，MVision系统在等中心处10 cGy的剂量下能够检测到一个2 cm大、电子密度对比度为1%的物体，并且配准软件在前后、左右和上下方向上的精度在2 mm以内。
