Institute of Clinical Research, University of Southern Denmark, Odense, Denmark.
Acta Oncol. 2012 Jul;51(6):752-8. doi: 10.3109/0284186X.2011.648341. Epub 2012 Jan 17.
Volumetric modulated arc therapy (VMAT) for treatment of non-small cell lung cancer (NSCLC) patients potentially changes the risk of radiation-induced pneumonitis (RP) compared to intensity modulated radiation therapy (IMRT) if the dose to the healthy lung is changed significantly. In this study, clinical IMRT plans were used as starting point for VMAT optimization and differences in risk estimates of RP between the two plan types were evaluated.
Fifteen NSCLC patients prescribed 66 Gy in 2 Gy fractions were planned with IMRT and subsequently with single arc VMAT. Dose metrics were evaluated for target and lung together with population averaged dose volume histograms. The risk of RP was calculated using normal tissue complication probability (NTCP) models. Finally, applicability of the plans was tested through delivery on an Elekta accelerator.
When changing from IMRT to VMAT only modest differences were observed in the dose to the lung and target volume. On average, fractions of lung irradiated to doses between 18 Gy and 48 Gy were statistically significant reduced using VMAT compared to IMRT. For the fraction of lung receiving more than 20 Gy the reduction was 1.2% percentage points: (range -0.6 -2.6%). The evaluated toxicity were smaller with VMAT compared to IMRT, however only modest differences were observed in the NTCP values. The plans were delivered without any problems. The average beam on time with VMAT was 83 s. This was a reduction of 141 s (ranging from 37 s to 216 s) compared to IMRT.
Using IMRT as reference for the VMAT optimization it was possible to implement VMAT in the clinic with no increase in estimated risk of RP. Thus, toxicity is not expected to be a hindrance to using VMAT and will profit from the shorter delivery time with VMAT compared to IMRT.
与强度调制放射治疗（IMRT）相比，容积调强弧形治疗（VMAT）治疗非小细胞肺癌（NSCLC）患者时，如果健康肺组织的剂量显著改变，可能会改变放射性肺炎（RP）的风险。在这项研究中，我们将临床 IMRT 计划作为 VMAT 优化的起点，并评估两种计划类型之间 RP 风险估计的差异。
对 15 例接受 2 Gy 分次 66 Gy 治疗的 NSCLC 患者进行 IMRT 计划和单弧 VMAT 计划。同时评估了靶区和肺的剂量学指标以及人群平均剂量体积直方图。采用正常组织并发症概率（NTCP）模型计算 RP 风险。最后，通过 Elekta 加速器进行了计划的适用性测试。
从 IMRT 改为 VMAT 时，肺和靶区的剂量仅有适度差异。与 IMRT 相比，VMAT 治疗时，18 Gy 至 48 Gy 剂量照射的肺部分数显著减少。对于接受超过 20 Gy 剂量的肺部分数，减少了 1.2%：（范围为-0.6%至 2.6%）。与 IMRT 相比，VMAT 治疗的毒性较小，但 NTCP 值仅有适度差异。计划的实施没有任何问题。VMAT 的平均射线照射时间为 83 s，与 IMRT 相比减少了 141 s（范围为 37 s 至 216 s）。
以 IMRT 为参考进行 VMAT 优化，可以在临床中实施 VMAT，而不会增加 RP 的风险估计。因此，与 IMRT 相比，VMAT 的较短治疗时间有望使毒性不会成为使用 VMAT 的障碍。
