The Value Of Defferent Images In Delineation Of Target Volume In Nasopharyngeal Carcinoma

Objective:Comparing CT,MRI and 18FDG-PET-CT in detecting tumor extension,lymph nodes,staging and delineating gross tumor volume(GTV)in nasopharyngeal carcinoma(NPC)to help to provide the optimal imaging examinations and advices of gross tumor volume delineation.Materials and Methods:From Sep.2006 to Noc.2006,34 consecutive patients with NPC diagnosed by pathology in radiothapy department of 1st affiliated hospital of guangxi medical university were enrolled.Contrast enhanced planning CT,MRI and 18FDG-PET-CT in treatment position were performed before treatment, then the datas were transferred to the treatment planning system(PS).All the images were read respectively in every case to define the tumor extension and stage,then sets of 4 GTVs were generated for each case by 4 methods: delimiting by CT(GTV_CT),delimiting by MRI(GTV_MRI),applying a threshold of 45%of the maximum standardized uptake value(SUVmax;GTV₄₅),and using an isocontour of SUV=2.5 around the tumor(GTV_2.5).The GTV of nasopharynx(GTVnx)was delineated respectively.Results:(1)In detecting the primary tumor extension,MRI was more clear than CT and 18FDG-PET-CT,but only the prestyloid space,longus scapitis and retropharyngeal lymph node were significantly different.MRI was higher than CT and 18FDG-PET-CT in the positive rates of retropharyngeal lymph node.In detecting the cervical lymph node metastasis,there had no statistical significance.PET was superior than MRI and CT in detecting the cervical lymph node metastasis which minimum diameter＜1cm..(2)Compared with CT,MRI made changes in 41.18%(14/ 34)of T stage(including 23.53%(8/34)up-staging and 17.65%(6/34) down-staging)for the Chinese'92 staging system,while made changes in 26.47%(9/34)of T stage(including 20.59%(7/34)up-staging and 5.88%(2 /34)down-staging)for the 6th edition UICC/AJCC staging system.(3)The GTVnxs decreased from GTV_CT(27.31±15.53cm3),GTV_MRI(26.30±17.93cm3),GTV_2.5(18.43±12.93cm3)and GTV₄₅(13.20±11.22cm3) respectively.There was statistical significance between GTV_CT/GTV_MRIand GTV_2.5/GTV₄₅.Compared with GTV_MRI,the GTV_CTwas larger(P=0.012)in early stages(T1,T2)and smaller in advanced stages(T3,T4).Conclusions:(1) In detecting the primary tumor extension of NPC,there are remarkable significances in longus scapitis,prestyloid space and retropharyngeal lymph node in MRI,CT and PET-CT.Compared with CT,MRI hasn't a remarkable advantage in detecting cervical lymph node metastasis.Compared with CT, MRI is more clear in detecting the invasion of longus scapitis,prestyloid space,base of skull,paranasal sinus,cavernous sinus and retropharyngeal lymph node,and 18FDG-PET-CT has no superiority.On the sum of cervical lymph node metastasis,CT is similar to MRI.Compared with CT and MRI, 18FDG-PET-CT has a remarkable advantage in detecting cervical lymph node metastasis which minimum diameter＜1cm.(2)In delineating GTVnx,with the standard of SUV=2.5 or 45%of SUVmax,the GTV delineating on PET is smaller than CT and MRI.There is no remarkable significance between CT and MRI in delineating GTVnx,but in the casese of T1+T2,GTV_CT＞.GTV_MRI,and there is remarkable significance.Compared with CT,MRI has a remarkable advantage in delineating GTVnx than CT in the view of images. 18FDG-PET-CT is only as an auxiliary examination and can afford some informations in guiding the delineation of GTVnx.