Reitz Bodo, Parda David S, Colonias Athanasios, Lee Vincent, Miften Moyed
Department of Radiation Oncology, Allegheny General Hospital, Pittsburgh, PA 15212, USA.
Med Dosim. 2009 Summer;34(2):158-69. doi: 10.1016/j.meddos.2008.07.001. Epub 2008 Aug 12.
Techniques for generating simplified IMRT treatment plans for treating non-small cell lung cancer (NSCLC) patients with respiratory motion were investigated. To estimate and account for respiratory motion, 4-dimensional computed tomography (4DCT) datasets from 5 patients were used to design 5-field 6-MV ungated step-and-shoot intensity modulated radiotherapy (IMRT) plans delivering a dose of 66 Gy to the planning target volume (PTV). For each patient, 2 plans were generated using the mean intensity and the maximum intensity of 10 CT datasets from different breathing phases. The plans also utilized different margins around the clinical target volume/internal target volume (CTV/ITV) to account for tumor motion. To reduce the treatment time and ensure accurate dose delivery to moving targets, the number of intensity levels was minimized while maintaining dose coverage to PTV and minimizing dose to organs at risk (OARs). Dose-volume histograms (DVHs), dosimetric metrics, and outcome probabilities were evaluated for all plans. Plans using the averaged CT image dataset were inferior, requiring larger margins around the PTV, with a maximum of 1.5 cm, to ensure coverage of the tumor, and therefore increased the dose to OARs located in proximity of the tumor. The plans based on superimposed CT image datasets achieved full coverage of the tumor, while allowing tight margins around the PTV and minimizing the dose to OARs. A small number of intensity-levels (3 to 5), resulting in IMRT plans with a total of 13 to 30 segments, were sufficient for homogeneous PTV coverage, without affecting the sparing of OARs. In conclusion, a technique involving treatment planning with the superimposed CT scans of all respiratory phases, and the application of IMRT with only a small number of segments was feasible despite significant tumor motion; however, greater patient numbers are needed to support the statistical significance of the results presented in this work.
研究了为患有呼吸运动的非小细胞肺癌（NSCLC）患者生成简化调强放疗（IMRT）治疗计划的技术。为了估计和考虑呼吸运动，使用了5名患者的4维计算机断层扫描（4DCT）数据集来设计5野6兆伏非门控步进式调强放疗（IMRT）计划，向计划靶区（PTV）给予66 Gy的剂量。对于每名患者，使用来自不同呼吸阶段的10个CT数据集的平均强度和最大强度生成2个计划。这些计划还利用临床靶区/内部靶区（CTV/ITV）周围的不同边界来考虑肿瘤运动。为了减少治疗时间并确保向移动靶区准确输送剂量，在保持对PTV的剂量覆盖并使危及器官（OARs）的剂量最小化的同时，将强度级别数量降至最低。对所有计划评估了剂量体积直方图（DVH）、剂量学指标和结果概率。使用平均CT图像数据集的计划较差，需要在PTV周围设置更大的边界，最大为1.5厘米，以确保肿瘤覆盖，因此增加了位于肿瘤附近的OARs的剂量。基于叠加CT图像数据集的计划实现了肿瘤的完全覆盖，同时允许在PTV周围设置紧密的边界并使OARs的剂量最小化。少量的强度级别（3至5个），产生总共13至30个射野的IMRT计划，足以实现PTV的均匀覆盖，而不影响对OARs的保护。总之，尽管肿瘤运动显著，但一种涉及使用所有呼吸阶段的叠加CT扫描进行治疗计划以及应用仅少量射野的IMRT的技术是可行的；然而，需要更多患者来支持本研究结果的统计学意义。
