Joint Department of Physics, The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, Sutton, Surrey, UK.
Phys Med Biol. 2011 Jul 21;56(14):4453-64. doi: 10.1088/0031-9155/56/14/014. Epub 2011 Jun 30.
Computed tomography images have been acquired using an experimental (low atomic number (Z) insert) megavoltage cone-beam imaging system. These images have been compared with standard megavoltage and kilovoltage imaging systems. The experimental system requires a simple modification to the 4 MeV electron beam from an Elekta Precise linac. Low-energy photons are produced in the standard medium-Z electron window and a low-Z carbon electron absorber located after the window. The carbon electron absorber produces photons as well as ensuring that all remaining electrons from the source are removed. A detector sensitive to diagnostic x-ray energies is also employed. Quantitative assessment of cone-beam computed tomography (CBCT) contrast shows that the low-Z imaging system is an order of magnitude or more superior to a standard 6 MV imaging system. CBCT data with the same contrast-to-noise ratio as a kilovoltage imaging system (0.15 cGy) can be obtained in doses of 11 and 244 cGy for the experimental and standard 6 MV systems, respectively. Whilst these doses are high for everyday imaging, qualitative images indicate that kilovoltage like images suitable for patient positioning can be acquired in radiation doses of 1-8 cGy with the experimental low-Z system.
已经使用实验性（低原子序数 (Z) 插入物）兆伏锥形束成像系统获取了计算机断层扫描图像。这些图像已与标准兆伏和千伏成像系统进行了比较。实验系统需要对 Elekta Precise 直线加速器的 4 MeV 电子束进行简单的修改。低能光子在标准中 Z 电子窗和位于窗后的低 Z 碳电子吸收器中产生。碳电子吸收器不仅能确保从源中去除所有剩余的电子，还能产生光子。还使用了对诊断 X 射线能量敏感的探测器。锥形束计算机断层扫描 (CBCT) 对比度的定量评估表明，低 Z 成像系统比标准 6 MV 成像系统优越一个数量级以上。实验性和标准 6 MV 系统的千伏成像系统（0.15 cGy）的相同对比度噪声比的 CBCT 数据，分别可以在 11 和 244 cGy 的剂量下获得。虽然这些剂量对于日常成像来说很高，但定性图像表明，实验性低 Z 系统可以在 1-8 cGy 的辐射剂量下获得适合患者定位的类似于千伏的图像。
