Sillanpaa Jussi, Chang Jenghwa, Mageras Gikas, Yorke Ellen, De Arruda Fernando, Rosenzweig Kenneth E, Munro Peter, Seppi Edward, Pavkovich John, Amols Howard
Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA.
Med Phys. 2006 Sep;33(9):3489-97. doi: 10.1118/1.2222075.
We report on the capabilities of a low-dose megavoltage cone-beam computed tomography (MV CBCT) system. The high-efficiency image receptor consists of a photodiode array coupled to a scintillator composed of individual CsI crystals. The CBCT system uses the 6 MV beam from a linear accelerator. A synchronization circuit allows us to limit the exposure to one beam pulse [0.028 monitor units (MU)] per projection image. 150-500 images (4.2-13.9 MU total) are collected during a one-minute scan and reconstructed using a filtered backprojection algorithm. Anthropomorphic and contrast phantoms are imaged and the contrast-to-noise ratio of the reconstruction is studied as a function of the number of projections and the error in the projection angles. The detector dose response is linear (R2 value 0.9989). A 2% electron density difference is discernible using 460 projection images and a total exposure of 13 MU (corresponding to a maximum absorbed dose of about 12 cGy in a patient). We present first patient images acquired with this system. Tumors in lung are clearly visible and skeletal anatomy is observed in sufficient detail to allow reproducible registration with the planning kV CT images. The MV CBCT system is shown to be capable of obtaining good quality three-dimensional reconstructions at relatively low dose and to be clinically usable for improving the accuracy of radiotherapy patient positioning.
我们报告了一种低剂量兆伏级锥形束计算机断层扫描（MV CBCT）系统的性能。高效图像接收器由耦合到由单个碘化铯（CsI）晶体组成的闪烁体的光电二极管阵列构成。CBCT系统使用来自直线加速器的6兆伏射线束。同步电路使我们能够将每次投影图像的曝光限制为一个射线束脉冲[0.028监测单位（MU）]。在一分钟扫描期间采集150 - 500幅图像（总计4.2 - 13.9 MU），并使用滤波反投影算法进行重建。对仿真人体模型和对比剂模型进行成像，并研究重建的对比噪声比与投影数量和投影角度误差的函数关系。探测器剂量响应呈线性（R2值为0.9989）。使用460幅投影图像和13 MU的总曝光量（对应患者最大吸收剂量约12 cGy）时，可分辨出2%的电子密度差异。我们展示了用该系统采集的首批患者图像。肺部肿瘤清晰可见，骨骼解剖结构观察得足够详细，以便与计划千伏CT图像进行可重复配准。结果表明MV CBCT系统能够在相对低剂量下获得高质量的三维重建，并且在临床上可用于提高放射治疗患者定位的准确性。
