大体积肺癌IMRT初次及二次计划剂量学变化研究

目的 采用刚性配准和形变配准方法获得大体积非小细胞肺癌(NSCLC) IMRT中靶区和危及器官(OAR)的累加剂量,并与初次计划的剂量进行比较。方法 选择 30例采用IMRT的大体积NSCLC患者,每位患者分别在放疗前和放疗20分次时进行4DCT模拟定位,基于初次4DCT的平均密度投影CT1-avg制定放疗计划为Plan1,基于二次4DCT的平均密度投影CT2-avg修改放疗计划为Plan2,分别采用刚性配准和形变配准方法将两次计划进行剂量累加得到Plan刚性和Plan形变。比较初次定位和二次定位之间大体肿瘤体积(GTV,以吸气末时相图像CT50%上的勾画为准)和OAR (OAR,以平均密度投影图像CTavg上的勾画为准)的体积变化,以及Plan2、Plan刚性、Plan形变的剂量体积指标相比Plan1的差异。结果 二次定位和初次定位相比,GTV、心脏体积分别缩小44.2%、5.5%,患侧肺、健侧肺、全肺体积分别增大5.2%、6.2%、5.8%(P<0.05);对于内GTV (IGTV,10个4DCT时相的GTV融合而来)和计划靶体积(PTV)的D95%、D98%、V100%,Plan2与Plan1相近(P>0.05),Plan刚性、Plan形变较Plan1均略有下降(P<0.05);对于脊髓、心脏、患侧肺、双肺剂量,Plan2、Plan刚性、Plan形变较Plan1均降低(P<0.05),其中心 脏V30Gy和 Dmean分别降低27.3%、16.5%、15.3%和15.2%、6.6%、5.6%,双 肺V20Gy和 Dmean分别降低15.6%、4.5%、3.7%和15.7%、6.2%、5.1%;Plan形变的IGTV和PTV的D95%、D98%,心 脏V40Gy,患侧肺和全肺 的V20Gy、Dmean高于Plan刚性(P<0.05)。形变配准后OAR相似指数明显高于刚性配准(P<0.05)。结论 Plan2中OAR剂量体积指标相比Plan1差别很大,因此它们在预测OAR放射性损伤方面均有较大偏差,而形变配准得到的剂量体积指标可以提高预测精度。

Study on dosimetric changes between initial and second treatment plans in IMRT for large volume NSCLC

Objective To evaluate the cumulative dose of the target volume and organs at risk (OARs) in intensity-modulated radiation therapy (IMRT) for large volume non-small cell lung cancer (NSCLC) based on rigid and deformation registration methods. The dosimetric changes between the initial and second treatment plans were compared. Methods Thirty patients treated with IMRT for large volume NSCLC with twice 4DCT scans acquired before radiotherapy and after 20 fractions of radiotherapy were recruited. The initial treatment plan (Plan1) based on the average density projection CT (CT1-avg) of the first 4DCT images and the second treatment plan (Plan2) based on the average density projection CT (CT2-avg) of the second 4DCT images were calculated. Then, the dose distributions of Plan1 and Plan2 were accumulated based on rigid and deformation registration methods to obtain Planrig and Plandef, respectively. Finally, the volume changes of gross tumor volume (GTV) and OARs between two CT scans were compared. The dose-volume parameters between Plan1 and other plans (including Plan2, Planrig and Plandef) were also statistically compared. Results Compared with the initial CT scan, the mean volume of GTV and heart on the second CT was decreased by 44.2% and 5.5%, respectively, while the mean volume of ipsilateral lung, contralateral lung and total lung was increased by 5.2%, 6.2% and 5.8%, respectively (all P<0.05). Compared with Plan1, the D95%, D98% and V100% of target volume IGTV (GTV fusion of 10 4DCT phases) and PTV in Plan2 did not significantly change (all P>0.05), and those in Planrig and Plandef were decreased (all P<0.05). The dose-volume parameters of spinal-cord, heart, ipsilateral lung and total lung in Plan2, Planrig and Plandef were significantly lower than those in Plan1(all P<0.05). Among them, the V30Gy and Dmean of heart were decreased by 27.3%, 16.5%, 15.3% and 15.2%, 6.6%, 5.6%, respectively. The V20Gy and Dmean of total lung were decreased by 15.6%, 4.5%, 3.7% and 15.7%, 6.2%, 5.1%, respectively. Some dose-volume parameters (including D95% and D98% of target volume, V40Gy of heart, V20Gy and Dmean of the ipsilateral lung and the total lung) of Plandef were higher than those in Planrig (all P<0.05). The Dice similarity coefficients (DSCs) of OARs after deformation registration were significantly higher than those after rigid registration (P<0.05). Conclusions The dose-volume parameters of OARs significantly differ between Plan1 and Plan2. Hence, all these parameters have a large degree of deviation in predicting radiation-induced injury of OARs. Nevertheless, the dose-volume parameters obtained by deformation registration can enhance the prediction accuracy.