RESUMO
Objective@#To evaluate the precision of image registration between MRI simulation (MRIsim) and CT simulation compared to diagnostic MRI(MRIdiag) and to provide information for further application of MRIsim.@*Methods@#A total of 24 patients who underwent both MRIsim and MRIdiag were enrolled, including 8 patients with gliomas, 8 with nasopharyngeal carcinomas and 8 with prostate cancers. MRIsim and MRIdiag images of each patient were fused with CT. The OARs were delineated on three modalities of images and targets were delineated on fusion image of MRIsim with CT (F_CTMsim) and fusion image of MRIdiag with CT (F_CTMdiag) respectively. The concordance index (CI), Dice′s similarity coefficient (DSC) between the OARs and image similarity index (S) based on images from MRIsim, MRIdiag and CT were evaluated. IMRT plans were designed based targets on F_CTMsim and OARs on CT images, and differences in dosimetry of targets and OARs were evaluated subsequently.@*Results@#Volumes of most OAR from three modalities of images showed no statistically significant difference(P>0.05). All the CI and DSC between the OARs derived from MRIsim and CT were higher than those corresponding values from MRIdiag, and a statistically significant difference was achieved in 50% of these OARs (t=2.58-5.47, P<0.05). The S values of MRIsim and MRIdiag compared with CT were 0.89 and 0.83 respectively (t=5.77, P<0.05). MRIsim improved the S value by 10% (2%-56%) compared with MRIdiag. No further differences in dosimetry were found on all OARs and all targets(P>0.05).@*Conclusions@#The precision of image registration can be significantly improved by introducing MRIsim into radiotherapy planning design compared with MRIdiag. However, no significant differences in dosimetry were found on targets produced by rigid registration and manual adjustment method .
RESUMO
Objective To investigate the role of large-diameter magnetic resonance imaging (MRI) simulation in target volume delineation in radiotherapy for nasopharyngeal carcinoma (NPC).Methods Eighteen patients with NPC underwent computed tomography (CT) simulation and MRI simulation scans and localization in the same body position,with SOMATOM Sensation Open 40-row 82-cm large-diameter CT simulator and Siemens 3T MRI MAGNETOM Skyra 70-cm large-diameter simulator,respectively.The gross tumor volume (GTV) and parotid glands were delineated on all images according to the ICRU Report 50/62,and MRI was applied to observe the changes in GTV and parotid volume during radiotherapy.Paired t-test was applied to analyze the differences between GTVCT and GTVMRI and between GTVnx-CT and GTVnx-MRI.Results GTVMRI decreased significantly compared with GTVCT,and the average volume decreased from (213.64±84.59) cm3 to (199.68±84.69) cm3(p=0.006).As for the volume of primary lesions in the nasopharynx,GTVnx-MRI was significantly smaller than GTVnx-CT,and the volume decreased from (95.75± 24.76) cm3 to (88.12±26.25) cm3 (P =0.001);as for the volume of cervical lymph nodes,GTVnd-MRI was significantly smaller than GTVnd-CT,and the volume decreased from (117.89± 72.69) cm3 to (111.56± 70.69) cm3 (P=0.018).The targets delineated by CT and MRI did not overlap completely,with major differences in skull base bone and cervical soft tissue.The volume of both parotid glands delineated on MRI image was higher than that delineated on CT image,with a major difference in the deep lobe.MRI showed that GTV was reduced by 82.64± 16.87％ during radiotherapy,and the volumes of the left and right parotid glands were reduced by (32.7± 23.95) ％ and (34.7± 21.72) ％,respectively.Conclusions The delineation of target volume based on MRI simulation is more accurate than that based on CT simulation and can achieve a smaller volume range,which helps to guide target volume delineation in radiotherapy for NPC accurately.