Moore C J, Amer A, Marchant T, Sykes J R, Davies J, Stratford J, McCarthy C, MacBain C, Henry A, Price P, Williams P C
North Western Medical Physics Department, Christie Hospital, Manchester M20 4BX, UK.
Br J Radiol. 2006 Sep;79 Spec No 1:S66-78. doi: 10.1259/bjr/68255935.
This paper offers a realistic review of kilovoltage X-ray cone beam tomography integrated with the treatment machine for image-guided radiotherapy in the light of experience taking a commercial system from prototype development into clinical use. It shows that key practicalities cannot be ignored, in particular the regular characterization of mechanical flex during gantry rotation, the mapping of defects in flat panel image transducers and their response to X-ray exposure. The number of X-ray projections and the doses required for clinically useful cone beam reconstruction at different therapy sites are considered in the context of imaging that is fit for purpose. Three roles for cone beam tomography in radiotherapy are identified: patient setup in three dimensions (3D), where even low dose cone beam tissue detail is superior to megavoltage imaging; disease targeting where, despite wide field scatter and slow scanning, it is possible to generate images that are suitable for tumour delineation even at challenging sites; adaptive treatment planning, where calibrated cone beam images have been shown to provide sufficient target detail to support "plan of the day" selection and have the potential for planning with bulk corrections. With frequent use in mind, the need to limit patient dose during setup, yet maximize much needed image quality in the target zone, is considered. Finally, it is noted that the development of cone beam tomography for radiotherapy is far from complete, with X-ray source, image transducer, reconstruction algorithms and techniques for image profile collection still being researched.
本文结合将商业系统从原型开发投入临床使用的经验，对与治疗机集成的千伏级X射线锥束断层扫描技术在图像引导放射治疗中的应用进行了实际评估。结果表明，一些关键的实际问题不容忽视，特别是在机架旋转过程中机械弯曲的定期表征、平板图像传感器中缺陷的映射及其对X射线照射的响应。在适合特定用途的成像背景下，考虑了不同治疗部位临床有用的锥束重建所需的X射线投影数量和剂量。确定了锥束断层扫描在放射治疗中的三个作用：三维（3D）患者摆位，即使低剂量锥束组织细节也优于兆伏级成像；疾病靶向，尽管存在宽视野散射和扫描速度慢的问题，但即使在具有挑战性的部位也有可能生成适合肿瘤轮廓勾画的图像；自适应治疗计划，已证明校准后的锥束图像能够提供足够的靶区细节以支持“当日计划”的选择，并且具有进行整体校正计划的潜力。考虑到频繁使用的情况，需要在摆位过程中限制患者剂量，同时在靶区最大化所需的图像质量。最后，需要指出的是，放射治疗用锥束断层扫描技术的发展远未完成，X射线源、图像传感器、重建算法以及图像轮廓采集技术仍在研究之中。
