非小细胞肺癌三维适形后程加速超分割放疗中肺剂量体积变化规律及临床意义探讨

Normal lung dose-volume histogram varieties in the former and later period of three dimensional conformal radiation therapy plans and their clinical significance in non-small cell lung cancer

目的分析肺癌前、后程三维适形计划中正常肺剂量体积直方图变化及其与两程计划合成结果比较，探讨正常肺剂量体积直方图变化规律及放疗中靶区修改的可行性。方法选择21例接受三维适形后程加速超分割放疗的非小细胞肺癌病例，设定首程（P1）、后程（P2）三维适形计划的处方剂量均为70Gy，V20≤35％。将P1按常规分割照射40Gy后，重新定位并修改靶区后设计P2，加速超分割照射30Gy。将P1靶区、射野和剂量（MU）等物理参数导入P_2CT定位图像中，与之合成得到70Gy合成计划（Pc）；计算首程和后程总肺体积、靶体积（GTV、PTV），计算首程、后程和合成计划中MLD、V，5、V10、T30。分析3种计划中各项指标变化规律，并单因素相关分析MLD和V20。结果前、后两程计划总肺体积无明显变化（t=0．19，P=0．850），后程GTV、PTV较首程明显缩小（t=2．88，P=0．009；t=4．01，P=0．001）。全组P2、P1的正常肺MLD分别为16．5、17．8Gy（t=2．60，P=0．017）、V30显著降低（t=2．19，P=0．041）；但V5、V10、V20相似。Pc较P1的肺MLD、V5、V10、V20、V30均相似。Pc较P2的肺MLD、V5、V10、V20、V30均明显增加。分层分析PTV缩小的14例患者P2、P1的V30、MLD显著降低（t=3．00，P=0．010；t=2．38，P=0．033），其中7例后程按首程射野数和相似入射角设计计划时V10V30显著减小（t=2．76，P=0．033；t=3．60，P=0．011）；Pc与P1比较各项指标相似，与P2比较明显增高。7例相差1～2射野和不同入射角的P1、P2和Pc之间各项指标相似。PTV不变或增大的7例P1和P2之间各项指标也相似。PTV增大或缩小显著影响MLD和V20（r=-0．62，P=0．03；r=0．48，P=0．029）。结论非小细胞肺癌在三维适形后程加速超分割放疗过程中肿瘤明显缩小时，修改靶区及计划可降低正常肺高剂量体积，如按相同射野方向时可能缩小正常肺低剂量体积。后程计划设计物理参数应与首程相似，融合计划评估全程计划正常肺剂量体积直方图比较合理。

Objective To analyze the normal lung dose-volume histogram（DVH） varieties in the former and later period（ P1 and P2 ）of three dimensional conformal radiation therapy（3DCRT） plans and the compound（ Pc ） plan in non-small cell lung cancer（ NSCLC）, and to access the feasibility to modify the target volume during the treatment course. Methods Twenty-one NSCLC patients who had received accelerated hyper-frationation 3DCRT in P2 were included in the study. Both of the PI and P2 plans were redesigned to a total dose of 70 Gy with V20 smaller than 35%. When the target volume was modified and P2 plan was redesigned using accelerated hyper-frationation 3 DCRT of 30 Gy after P1 plan of 40 Gy, the Pc plan was compounded by transmitting the parameters （such as target volume, irradiation field and dose） of P1 plan into P2 plan. Total lung volume and target volumes （GTV, PTV） of P1 and P2 were evaluated. MLD, V5, V10, V20 and V30 of P1 ,P2 and Po were calculated. Results The total lung volume in P1 and P2 plans was not significantly different（t =0.19,P=0.850）. The volumes of GTV,PTV in P2 were obviously smaller than P1 （t=2.88,P=0.009;t=4.01, P=0.001）. When comparing P2 with P1, MLD were 16.5 Gy Vs 17.8 Gy （t=2.6 0,P=0.017）, V30 was significantly decreased （ t = 2.19, P = 0. 041 ）, but V5, V10 and V20 had no significant difference. Similar differences were found in MLD,V5 ,V10 ,V20 and V30 when comparing Pc to P1. P2 plans had significantly smaller MLD, V5 , V10, V20 and V30 than Pc plans. Fourteen patients with decreased PTV were further analyzed. The V30 and MLD decreased significantly （ t = 3.00, P = 0.010 ;t = 2.38, P = 0.033 ）, but V5 ,V10 ,V20 had no difference when comparing P1 and P2 plans. Among these 14 patients,the V10 and V30 decreased significantly（ t = 2.76, P = 0. 033 ; t = 3.60, P = 0.011 ） when P2 plans were generated using the same field number and beam angles in P1 plans in 7 patients. The parameters were similar in Pl and Po plans,but increased significantly when comparing to P2. Various parameters were the same among P1, P2 and Pc plans when P2 plans were designed using 1-2 different fields and angles in the other 7 patients. The differences were not significant between Pl and P2 plans in 7 patients with the same or increased PTV. Expansion or contraction of PTV significantly influenced MLD and V20 （ r = - 0.62, P = 0.03 ; r = 0.48, P = 0. 029）. Conclusions When the tumor regresses, the high dose volume of the lung decreases with modifying the target volume and replanning in the later period using accelerated hyper-frationation 3DCRT. The low dose volume of the lung may decrease if the field orientations are same throughout the treatment. It is rational to eval- uate the normal lung DVH of the whole plan when the physical parameters of the later period plan are the same as the former one.