Difference Of Target Delineation Between MRI Images And Localized CT Images Before Brachytherapy For Cervical Cancer And Feasibility Of CT-based Brachytherapy Plan

Objective:In order to contrast the distinction of tumor target delineation between diagnostic MRI and CT before three-dimensional brachytherapy in cervical cancer,and to explore the feasibility of three-dimensional brachytherapy with CT localization in cervical cancer.Methods:A total of 100 patients with cervical cancer who met the inclusion and exclusion criteria of simultaneous radiotherapy and chemotherapy in our hospital from 2018 to2019 were analyzed retrospectively.According to the GEC-ESTRO target area delineation recommendations,the differences of gross tumor volume(GTVres),width(left and right diameter),thickness(anterior and posterior diameter)and height(upper and lower diameter)on diagnostic MRI images and CT images were compared.The dose of the target area(GTVres,HR-CTV)and organs at risk(bladder,rectum,sigmoid colon),EQD2 and related radiation side effects of CT radiotherapy plan were evaluated.The optimal Cutoff value(3.48cm3)of target volume GTVres on MRI images was obtained by ROC curve analysis.Patients were divided into small volume group and large volume group.Paired sample T test was used for target volume dose and chi-square test was used for toxicity and side effects.Results:The Cutoff value of ROC curve of target volume on MRI image is 3.48cm3,and the Cutoff value is divided into groups.In the small volume group,there was no difference in target volume,width,thickness and height between MRI and CT,which were(2.83±0.48:3.19±1.28)cm~3,(1.90±0.34:2.13±0.68)cm,(1.60±0.40:1.65±0.77)cm,(1.63±0.33:1.84±1.24)cm(P>0.05),respectively.In the large group,GTVres,width,thickness and height of MRI were smaller than those of CT,which were(5.89±1.77:9.77±4.73)cm~3,(1.96±0.46:3.23±1.06)cm,(1.78±0.44:2.22±0.82)cm,(1.79±0.44:2.72±1.11)cm,(P=0.000),respectively.There was no difference in target GTVres and HR-CTV between small volume group and large volume group,which were(5.26±0.56,5.41±0.41)Gy:(5.12±0.33、5.36±0.36)Gy,respectively.There was no difference in EQD2,which was(100.19±4.95,91.27±4.35)Gy:(99.96±3.77,90.78±3.81)Gy,respectively.There was no difference in bladder D1cm3,bladder D2cm3,rectal D1cm3,rectal D2cm3,sigmoid colon D2cm3 between small volume group and large volume group,They were[(3.04±0.27)Gy,(2.81±0.24)Gy,(2.96±0.35)Gy,(2.66±0.33)Gy,(1.62±0.28)Gy]:[(3.09±0.44)Gy,(2.87±0.41)Gy,(2.98±0.48)Gy,(2.69±0.44)Gy,(1.96±0.35)Gy,all P>0.05].No different in EQD2between bladder,straight intestine and colon sigmoideum,They were[(79.89±2.84)Gy,(69.97±2.91)Gy,(61.43±6.35)Gy]:[(80.49±4.67)Gy,(70.28±3.81)Gy,(63.85±4.84)Gy,all P>0.05].The CT localized radiotherapy plan meets the recommendations of GEC-ESTRO in terms of target coverage and organ dose limitation.The incidence of acute/chronic radiation side effects in the small volume group was lower than that in the large volume group,but the difference was not statistically significant.Conclusions:For the small volume patients whose tumor volume is less than 3.48cm~3on diagnostic MRI images before three-dimensional brachytherapy,there is no difference between MRI images and CT images.The target area of radiotherapy planning and the dose limit of organs at risk are all up to the recommended standard of GEC-ESTRO.CT localization can be used instead of MRI localization.For patients with large tumor volume≥3.48cm3,the target area delineated by MRI image is smaller than that by CT image,so it is suggested that MRI localization should be preferred.However,the CT localization of the target area of radiotherapy planning and the dose limit of organs at risk are up to the recommended standards of GEC-ESTRO.When the condition is limited,MRI localization can not be performed,CT localization of radiotherapy planning is also feasible.