Mri And Ct Comparative Study Of Nasopharyngeal Carcinoma Staging And Radiation Treatment Planning

Objective:To compare the image of magnetic resonance imaging(MRI)and computed tomography(CT)in assessing nasopharyngeal carcinoma(NPC),and to evaluate the value of MRI and CT in clinical T-staging system(Chinese 1992 staging system)of NPC.To study the gross target volume(GTV),clinical target volume one(CTV1)and clinical target volume two(CTV2)of primary rumor influenced by MRI and CT skull base image difference based on above results. To analyze the dose of three-dimensional conformal RT(3-DCRT)influenced by MRI and CT skull base image difference.Methods:One hundred and one cases of primary NPC,histologically diagnosed and received enhanced spiral CT and MRI scans of nasopharynx were enrolled in this study.The MRI findings were compared to those obtained by CT scans.T-staging system of NPC influenced by MRI and CT image difference were analyzed.Twenty six cases(25.7%,twenty six cases in one hundred and one cases)of MRI and CT image difference at the skull base were delineated and compared the gross target volume(GTV)of primary tumor(NPC)by ARTP-TOP 3D-TPS system made in America.To investigate the skull base image difference between MRI and CT scans of nasopharyngeal carcinoma in gross target volume(GTV).Gross target volume(GTV),clinical target volume one(CTV1),clinical target volume two(CTV2)and critical organ at risk(brain stem,spinal cord,temporal lobe and eyeball)were outlined in ten cases according to CT and MRI image.3D-CRT plans were developed by contouring the treated area with CT and MRI image respectively,which difference were compared in affecting critical organ at risk.Results:(1)MRI was superior to CT in demonstrating lesions in the retropharyngeal node,musculus longus capitis,cavilla,basilar clivus,cavernous sinuses and paranasal sinuses.(2)The cases distribution of clinical T-staging proved by MRI was:1 T1,37 T2,43 T3,20 T4;which proved by CT was:4 T1, 63 T2,23 T3,9 T4.There was a statistic difference in the cases distribution of clinical T-staging proved by MRI and CT(P=0.0000343).(3)In twenty six cases,the target volume of primary tumor delineated in MRI and CT image were 46.62±11.54 and 34.67±8.53 respectively.There was a statistic difference in target volume of primary tumor(P＜0.001).(4)To evaluate the radiation dosimetry,target volume and critical organ at risk were outlined in ten cases according to CT and MRI image.3D-CRT plans were developed by using ARTP-TOP 3D-TPS system.Compared with CT,the MRI-based target volume (GTV,CTV1 and CTV2)was larger,and both the average radiation dose and the maxium radiation dose of the MRI-based critical organ at risk(brain stem, temporal lobe and eyeball)were higher except spinal cord.Conclusions:(1)MRI was superior to CT in demonstrating lesions in the retropharyngeal node,musculus longus capitis,cavilla,basilar clivus,cavernous sinuses and paranasal sinuses.(2)In T-staging system of NPC,the constituent ratio of early stages(T1,T2)in MRI is lower than that in CT assessment,while the constituent ratio of terminal stages(T3,T4)in MRI is higher than CT assessment.(3)In the cases invaded at the skull base proved by MRI,the target volume(GTV,CTV1 and CTV2)of primary tumor delineated by MPd image were larger than by CT image(GTV_MR>GTV_CT,CTV1_MR>CTV1_CT,CTV2_MR >CTV2_CT),which will influence the clinical radiotherapy plan.(4)The evaluation of radiation dosimetry suggests that,for MRI-based targets,3D-CRT plans achieved adequate target coverage,but the dose to critical organ at risk was significantly worse in some cases which MRI and CT image was different at the skull base.For these cases,aiming at target dose uniformity and sparing of critical organ at risk,intensity modulated radiation therapy(IMRT)plan was obviously superior to 3D-CRT plan.