| Objective1.To analyze the set-up errors of EPID and CT on rail system in image-guided radiation therapy(IGRT)for cervical cancer and evaluate the application value of CT on rail system in IGRT for cervical cancer;2.To analyze the effects of different filling states on the dose distribution of target and oagans at risk(OAR)in IGRT for cervical cancer by CT on rail.Methods15 patients with cervical cancer were selected in the study.First,EPID images and CT on rail images were taken once a week in the bladder filling state(emptying the bladder 2hours before positioning and a one-time drinking water 500ml).We obtained different set-up errors in X,Y,Z axis though comparing EPID images with the DDR,matching CT on rail images with planned CT images by grey alignment and bone alignment.We had the three sets of data for statistical analysis,and calculated the CTV-PTV outgoing pitch(MPTV)in each direction.Then we taken CT on rail images in the bladder emptying state,and transmitted the two obtained CT images to the three-dimensional treatment planning system(TPS),performed the treatment plan.Finally,we obtained the two groups dose parameters of clinical target volume(CTV)and rectum,bladder in the bladder filling and empty state,and we had all data for statistical analysis.Results1.The set-up errors measured by EPID,CT on rail bone and grayscale in X-axis were0.251 ± 0.065,0.209 ± 0.536,0.184 ± 0.046 cm,in Y-axis were 0.379 ± 0.044,0.256 ±0.060,0.204 ± 0.051 cm,and in Z-axis were 0.185 ± 0.051,0.112 ± 0.057,0.126 ±0.058 cm.Compared with EPID group,the set-up errors of grey alignment and bone alignment group were significantly reduced in X,Y,Z axis(P<0.05),and those of were also significantly lessened(P<0.05).Besides,the set-up errors of grey alignment group in X,Y axis were less than those of bone alignment group,especially in Y axis(P<0.05),and those in axis were similar.The MPTV of the three groups in the X axis were0.67,0.56 and 0.49 cm,in Y axis were 0.98,0.68 and 0.54 cm,and in Z axis were0.50,0.32,0.35 cm.2.Comparing the bladder filling with emptiness in IGRT for cervical cancer,CTV average dose(CTV Dmean)were 5057.50 ± 91.09,5039.08 ± 88.31 c Gy,and the maximum dose of CTV(CTV D2)was 5353.50 ± 64.20,5341.05 ± 70.37 c Gy.There were no significant differences between the two groups(P> 0.05);The bladder average dose(bladder Dmean)were 3606.00 ± 146.36,4093.00 ± 151.81 c Gy.V40% of the bladder were 36.50 ± 5.16,49.70 ± 8.51,V45% were 24.75 ± 6.42,27.28 ± 6.63,and V50% were12.42±2.23,12.90±2.42.There were significant differences in bladder Dmean,V40 and V45(P <0.05),but significant differences in bladder V50 were not there(P>0.05);The rectum average dose(rectum Dmean)were 3738.50± 257.45,3804.00±309.18 c Gy.V40% of the rectum were 44.78±6.73,55.23±5.67,V45% were 30.15±4.74,31.90±5.04,and V50% were 5.52 ±0.27,5.64±0.45.The differences in rectum Dmean,V40 and V45 were significant(P <0.05),but those of rectum V50 were not significant(P> 0.05).Conclusions1.CT on rail system is better than EPID in measuring the set-up errors in IGRT for cervical cancer,which made the target more accurate.During the IGRT for cervical cancer guided by CT on rail,grey alignment was better than bone alignment.We can used the MPTV as a reference for radiotherapy of cervical cancer in this center,which calculated according to the set-up errors measured by grey alignment of CT on rail;2.During the IGRT for cervical cancer guided by CT on rail,bladder filling state was conducive to the protection of OAR,such as bladder and rectum,and we should try to keep the bladder filling state in each treatment. |
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