Department of Radiation Oncology and Division of Medical Radiation Physics, Inselspital, Bern University Hospital, and University of Bern, Bern, Switzerland.
Radiat Oncol. 2017 Jun 20;12(1):102. doi: 10.1186/s13014-017-0838-4.
The aim was to evaluate the geometric and corresponding dosimetric differences between two delineation strategies for head and neck tumors neighboring air cavities.
Primary gross and clinical tumor volumes (GTV and CTV) of 14 patients with oropharynx or larynx tumors were contoured using a soft tissue window (S). In a second strategy, the same volumes were contoured with an extension to include the parts which became visible on lung window (L). For the calculation of Hausdorff-distances (HD) between contoured volumes of the two strategies, triangular meshes were exported. Two radiotherapy plans with identical goals and optimization parameters were generated for each case. Plan_S were optimized on CTV_S, and Plan_L on CTV_L. The dose coverages of CTV_L and CTV_Δ (CTV_L minus CTV_S) were evaluated in Plan_S. OAR doses were compared among Plan_S and Plan_L.
Median three-dimensional HD for GTVs and CTVs were 5.7 (±2.6) and 9.3 (±2.8) mm, respectively. The median volume differences between structures contoured using L and S windows were 9% (±5%) and 9% (±4%) for GTV and CTV, respectively. In 13 out of 14 cases, Plan_S met the plan acceptance criteria for CTV_L. In 8 cases CTV_Δ was covered insufficiently in Plan_S. Mean and median differences in OAR dose-volume histogram parameters between Plan_S and Plan_L were within 3%.
For the current practice in radiotherapy planning for head and neck cancer, the delineation of L-based volumes seems unnecessary. However, in special settings, where smaller or no PTV margins are used, this approach may play an important role for local control.
本研究旨在评估两种勾画策略在勾画毗邻空气腔的头颈部肿瘤时的几何形状和相应剂量学差异。
14 例口咽或喉癌患者的原发大体肿瘤体积（GTV）和临床靶区体积（CTV）采用软组织窗（S）进行勾画。在第二种策略中，采用扩展的方法将可见于肺窗（L）的部分也包括进来进行勾画。为了计算两种策略勾画的体积之间的 Hausdorff 距离（HD），导出了三角网格。为每个病例生成了两个具有相同目标和优化参数的放疗计划。Plan_S 是在 CTV_S 上进行优化的，Plan_L 是在 CTV_L 上进行优化的。在 Plan_S 中评估了 CTV_L 和 CTV_Δ（CTV_L 减去 CTV_S）的剂量覆盖情况。比较了 Plan_S 和 Plan_L 之间的 OAR 剂量。
GTV 和 CTV 的三维 HD 的中位数分别为 5.7（±2.6）和 9.3（±2.8）mm。使用 L 和 S 窗勾画结构时，GTV 和 CTV 的中位数体积差异分别为 9%（±5%）和 9%（±4%）。在 14 例病例中，有 13 例 Plan_S 满足 CTV_L 的计划接受标准。在 8 例病例中，Plan_S 中 CTV_Δ 的覆盖不足。Plan_S 和 Plan_L 之间 OAR 剂量-体积直方图参数的平均和中位数差异均在 3%以内。
对于目前头颈部癌症放射治疗计划的实践，基于 L 勾画体积似乎没有必要。然而，在使用较小或没有 PTV 边界的特殊情况下，这种方法可能对局部控制发挥重要作用。
