Section for Biomedical Physics, University Hospital for Radiation Oncology, Eberhard-Karls-University Tübingen, Hoppe-Seyler-Str. 3, 72076 Tübingen, Germany.
Phys Med. 2013 Nov;29(6):644-9. doi: 10.1016/j.ejmp.2012.08.002. Epub 2012 Sep 10.
Combined PET/CT imaging has been proposed as an integral part of radiotherapy treatment planning (TP). Contrast-enhanced CT (ceCT) images are frequently acquired as part of the PET/CT examination to support target delineation. The aim of this dosimetric planning study was to investigate the error introduced by using a ceCT for intensity modulated radiotherapy (IMRT) TP with Monte Carlo dose calculation for non-small cell lung cancer (NSCLC).
Nine patients with NSCLC prior to chemo-RT were included in this retrospective study. For each patient non-enhanced, low-dose CT (neCT), ceCT and [(18)F]-FDG-PET emission data were acquired within a single examination. Manual contouring and TP were performed on the ceCT. An additional set of independent target volumes was auto-segmented in PET images. Dose distributions were recalculated on the neCT. Differences in dosimetric parameters were evaluated.
Dose differences in PTV and lungs were small for all patients. The maximum difference in all PTVs when using ceCT images for dose calculation was -2.1%, whereas the mean difference was less than -1.7%. Maximum differences in the lungs ranged from -1.8% to 2.1% (mean: -0.1%). In four patients an underestimation of the maximum spinal cord dose between 2% and 3.2% was observed, but treatment plans remained clinically acceptable.
Monte Carlo based IMRT planning for NSCLC patients using ceCT allows for correct dose calculation. A direct comparison to neCT-based treatment plans revealed only small dose differences. Therefore, ceCT-based TP is clinically safe as long as the maximum acceptable dose to organs at risk is not approached.
正电子发射断层扫描/计算机断层扫描（PET/CT）联合成像已被提议作为放射治疗计划（TP）的一个组成部分。对比增强 CT（ceCT）图像常作为 PET/CT 检查的一部分获取，以支持靶区勾画。本剂量学计划研究的目的是研究在非小细胞肺癌（NSCLC）调强放疗（IMRT）TP 中使用 ceCT 进行蒙特卡罗剂量计算时引入的误差。
本回顾性研究纳入了 9 例接受化疗-放疗前的 NSCLC 患者。对于每位患者，在单次检查中采集非增强低剂量 CT（neCT）、ceCT 和 [(18)F]-FDG-PET 发射数据。在 ceCT 上进行手动勾画和 TP。在 PET 图像上自动分割另一组独立的靶区。在 neCT 上重新计算剂量分布。评估剂量学参数的差异。
所有患者的 PTV 和肺的剂量差异较小。当使用 ceCT 图像进行剂量计算时，所有 PTV 的最大差异为-2.1%，而平均差异小于-1.7%。肺的最大差异范围为-1.8%至 2.1%（平均：-0.1%）。在 4 例患者中，观察到最大脊髓剂量低估了 2%至 3.2%，但治疗计划仍具有临床可接受性。
使用 ceCT 对 NSCLC 患者进行基于蒙特卡罗的 IMRT 计划可实现正确的剂量计算。与基于 neCT 的治疗计划的直接比较仅显示出较小的剂量差异。因此，只要不接近危及器官的最大可接受剂量，ceCT 基 TP 就是临床安全的。
