Department of Radiation Oncology, University of Heidelberg, Mannheim, Germany.
Radiother Oncol. 2012 Feb;102(2):268-73. doi: 10.1016/j.radonc.2011.10.006. Epub 2011 Nov 17.
PURPOSE/OBJECTIVE(S): IMRT allows dose escalation for large lung tumors, but respiratory motion may compromise delivery. A treatment plan that modulates fluence predominantly in the transversal direction and leaves the fluence identical in the direction of the breathing motion may reduce this problem.
MATERIALS/METHODS: Planning-CT-datasets of 20 patients with Stage I-IV non small cell lung cancer (NSCLC) formed the basis of this study. A total of two IMRT plans and one 3D plan were created for each patient. Prescription dose was 60 Gy to the CTV and 70 Gy to the GTV. For the 3D plans an energy of 18 MV photons was used. IMRT plans were calculated for 6 MV photons with 13 coplanar and with 17 noncoplanar beams. Robustness of the used method of anisotropic modulation toward breathing motion was tested in a 13-field IMRT plan.
As a consequence of identical prescription doses, mean target doses were similar for 3D and IMRT. Differences between 3D and 13- and 17-field IMRT were significant for CTV Dmin (43 Gy vs. 49.1 Gy vs. 48.6 Gy; p<0.001) and CTV D(95) (53.2 Gy vs. 55.0 Gy vs. 55.4 Gy; p=0.001). The D(mean) of the contralateral lung was significantly lower in the 17-field plans (17-field IMRT vs. 13- vs. 3D: 12.5 Gy vs. 14.8 Gy vs. 15.8 Gy: p<0.05). The spinal cord dose limit of 50 Gy was always respected in IMRT plans and only in 17 of 20 3D-plans. Heart D(max) was only marginally reduced with IMRT (3D vs. 13- vs. 17-field IMRT: 38.2 Gy vs. 36.8 Gy vs. 37.8 Gy). Simulated breathing motion caused only minor changes in the IMRT dose distribution (~0.5-1 Gy).
Anisotropic modulation of IMRT improves dose delivery over 3D-RT and renders IMRT plans robust toward breathing induced organ motion, effectively preventing interplay effects.
调强适形放疗（IMRT）允许对大的肺部肿瘤进行剂量递增，但呼吸运动可能会影响治疗的实施。一种在横断方向上主要调节射束强度而在呼吸运动方向上保持射束强度一致的治疗计划可能会减少这个问题。
本研究基于 20 例 I 期-IV 期非小细胞肺癌（NSCLC）患者的计划-CT 数据集。为每位患者分别创建了 2 个调强适形放疗计划和 1 个三维计划。CTV 的处方剂量为 60 Gy，GTV 的处方剂量为 70 Gy。三维计划采用 18 MV 光子能量，调强适形放疗计划采用 6 MV 光子，有 13 个共面射束和 17 个非共面射束。在 13 野调强适形放疗计划中测试了各向异性调制对呼吸运动的稳健性。
由于处方剂量相同，三维和调强适形放疗的平均靶区剂量相似。CTV Dmin（43 Gy 比 49.1 Gy 比 48.6 Gy；p<0.001）和 CTV D（95）（53.2 Gy 比 55.0 Gy 比 55.4 Gy；p=0.001）的三维与 13 野和 17 野调强适形放疗计划之间存在显著差异。对侧肺的 Dmean（17 野调强适形放疗比 13 野比三维：12.5 Gy 比 14.8 Gy 比 15.8 Gy；p<0.05）显著降低。脊髓 50 Gy 剂量限制在调强适形放疗计划中始终得到遵守，而在三维计划中仅在 20 个计划中的 17 个中得到遵守。心脏 Dmax 仅略有降低（三维比 13 野比 17 野调强适形放疗：38.2 Gy 比 36.8 Gy 比 37.8 Gy）。模拟呼吸运动仅导致调强适形放疗剂量分布发生轻微变化（约 0.5-1 Gy）。
IMRT 的各向异性调制可改善三维适形放疗的剂量传递，并使 IMRT 计划对呼吸运动引起的器官运动具有稳健性，有效防止相互作用效应。
