基于形变配准分析18例鼻咽癌放疗中肿瘤靶区和危及器官剂量变化

目的在鼻咽癌调强放疗过程中,靶区和危及器官的体积不断变化,可能导致其实际接受剂量与初次计划剂量不一致。本研究通过形变配准方法获得2次计划的累积剂量,为预测鼻咽癌调强放疗的治疗反应提供参考。方法收集2014-07-08-2018-05-02山东省肿瘤医院放疗科收治的18例进行同步加量调强放疗的鼻咽癌患者,在定位图像CT1上制定初次放疗计划Plan1,在治疗20~25分次后的复位图像CT2上制定放疗计划Plan2。利用Velocity将Plan2剂量与Plan1剂量分别刚性和形变配准累加得到Plan刚性和Plan形变。比较靶区和危及器官在Plan1、Plan2、Plan刚性和Plan形变的剂量-体积指标变化。结果18例鼻咽癌患者CT1和CT2中大体肿瘤靶区(gross tumor volume,GTV)分别为(79.28±49.66)和(64.47±42.39)cm3,Z=-3.724,P<0.001;左腮腺体积分别为(16.76±4.74)和(10.77±4.07)cm3,Z=-3.724,P<0.001;右腮腺体积分别为(16.63±4.40)和(10.46±3.99)cm3,Z=-3.724,P<0.001。形变配准左腮腺(t=5.158,P<0.001)、右腮腺(t=7.808,P<0.001)、左视神经(t=2.664,P=0.016)和脊髓(t=4.660,P<0.001)相似指数与刚性配准比较,差异有统计学意义。Plan2与Plan1相比,左右腮腺的V30以及脑干、左右眼球、左右晶状体、左右视神经的Dmax均下降,平均下降17.0%~60.1%。Plan形变与Plan1相比,GTV和肿瘤计划靶区(plan gross tumor volume,PGTV)的Dmean、D99,腮腺Dmean以及眼球和视神经Dmax变化均<5%。Plan刚性与Plan1相比,GTV和PGTV的Dmean、D95,腮腺Dmean、V30、D50以及眼球和视神经Dmax变化均<10%。结论鼻咽癌调强放疗过程中,肿瘤靶区及腮腺体积缩小,形变累加后靶区和危及器官各项剂量-体积指标与初次计划基本相当,因此初次计划的剂量-体积指标可以预测放疗过程中的疗效和放射性损伤。

Variation of dose-volume parameters for tumor target volumes and organs at risk in 18 cases of nasopharyngeal carcinoma during radiotherapy based on deformation registration

OBJECTIVE During intensity modulated radiation therapy(IMRT)for nasopharyngeal carcinoma(NPC),the volume of the target volume and the organ at risk(OAR)will change constantly.which may lead to the inconsistency between the actual dose received and the initial planned dose.In this study,the cumulative dose of the two plans was obtained by deformable registration,which can be used to predict the response to intensity modulated radiotherapy for NPC.METHODS From July 8 th,2014 to May 2 nd,2018,eighteen NPC patients who accepted simultaneous integrated boost intensity-modulated radiotherapy(SIB-IMRT)were enrolled.All patients underwent simulation CT(CT1)and replanning CT(CT2)scan after 20-25 fractions of radiation therapy.The treatment plans were designed on CT1 and CT2 and that were called Plan1 and Plan2 respectively.The Planreg and Plandef were obtained after registering from CT2 to CT1 using rigidity and deformation technology by Velocity.The dose-volume parameters differences on gross tumor volume(GTV)and OARs among Plan1,Plan2,Planrig and Plandef were compared.RESULTS The gross tumor target volume of CT1 and CT2 in 18 patients with nasopharyngeal carcinoma were(79.28±49.66)and(64.47±42.39)cm3,Z=-3.724,P<0.001.The left parotid gland volume was(16.76±4.74)and(10.77±4.07)cm3,Z=-3.724,P<0.001,and the right parotid gland volume was(16.63±4.40)and(10.46±3.99)cm3,Z=-3.724,P<0.001,respectively.The similarity index of deformation registration for left parotid gland(t=5.158,P<0.001),right parotid gland(t=7.808,P<0.001),left optic nerve(t=2.664,P=0.016)and spinal cord(t=4.660,P<0.001)was significantly different from rigid registration.Compared with Plan1,V30 in left and right parotid gland,Dmaxin brain stem,left and right eyeballs,left and right lens and left and right optic nerve decreased by 17.0%-60.1% on average.Compared with Plan1,Dmean,D99,Dmeanin parotid gland,Dmaxin eyeball and optic nerve of GTV and plan gross tumor volume(PGTV)were less than 5%.Compared with Plan1,the changes of Dmean,D95,Dmean,V30,D50 of parotid gland and Dmaxof eyeball and optic nerve of GTV and PGTV were less than 10%.CONCLUSIONS During the course of IMRT for cases with NPC,the volume of GTV and parotid gland were decreased.The dose-volume indexes of the GTV and the OARs in Plandef were similar to that in Plan1.Therefore,the dose-volume index of Plan1 can be used to evaluate the efficacy of radiotherapy and to predict radioactive damage.