de Koste John R van Sörnsen, Lagerwaard Frank J, de Boer Hans C J, Nijssen-Visser Margriet R J, Senan Suresh
Department of Radiation Oncology, Erasmus Medical Center, Rotterdam, The Netherlands.
Int J Radiat Oncol Biol Phys. 2003 Apr 1;55(5):1394-9. doi: 10.1016/s0360-3016(02)04602-3.
Lung tumors located in the lower lobe are the most mobile. Multiple computed tomographic (CT) scans, which had been performed for radiotherapy planning, were analyzed to determine the minimal number of required scans.
Six spiral CT scans (3 rapid and 3 slow) from 7 such patients were coregistered. Reproducibility of target volumes was defined as the ratio between the overlapping and encompassing volume (COM/SUM) from scans derived using one technique. Volumetric and dosimetric analyses were performed.
Slow CT scans generated larger and more reproducible target volumes than rapid planning scans, with a mean COM/SUM ratio of 71.9 +/- 8.7% and 58.0 +/- 12.7%, respectively. When only a single slow CT scan was used for planning, the addition of a symmetrical 3D margin of 5 mm ensured 99% coverage of the "optimal" target volume, which was derived from summation of target volumes from all six scans.
Planning target volumes (PTVs) derived from a single slow CT scan plus a 5-mm margin covered the "optimal" PTVs generated from six scans. Although these "slow PTVs" were larger, the increase in V(20) (the volume of lung tissue receiving a dose > or = 20 Gy) was limited. This indicates that only two CT scans, i.e., a full rapid scan of the entire thorax and a limited slow scan, are necessary for treatment planning in peripheral lung cancers.
位于下叶的肺部肿瘤活动度最大。分析为放疗计划而进行的多次计算机断层扫描（CT），以确定所需的最少扫描次数。
对7例此类患者的6次螺旋CT扫描（3次快速扫描和3次慢速扫描）进行配准。靶区体积的可重复性定义为使用一种技术获得的扫描中重叠体积与包含体积之比（COM/SUM）。进行了体积分析和剂量分析。
慢速CT扫描生成的靶区体积比快速计划扫描更大且更具可重复性，平均COM/SUM比值分别为71.9±8.7%和58.0±12.7%。当仅使用一次慢速CT扫描进行计划时，添加5mm的对称三维边界可确保99%覆盖“最佳”靶区体积，该体积是通过将所有六次扫描的靶区体积相加得出的。
由一次慢速CT扫描加上5mm边界得出的计划靶区体积（PTV）覆盖了由六次扫描生成的“最佳”PTV。尽管这些“慢速PTV”更大，但V(20)（接受剂量≥20Gy的肺组织体积）的增加是有限的。这表明在外周型肺癌的治疗计划中，仅需两次CT扫描，即对整个胸部进行一次完整的快速扫描和一次有限的慢速扫描。
