Purpose:To investigate the cumulative dose delivered to the High-risk clinical target volume(HR-CTV)throughout the course of cervix cancer treatment with external beam radiotherapy(EBRT)and brachytherapy(BT).Methods:Twenty-two cervical cancer patients,FIGO stage IB2 to IVA,were retrospectively analyzed.Between October 2012 and June 2014,all patients were treated to a total dose of 45 Gy in 25 fractions using EBRT,intensity-modulated radiation therapy(IMRT),followed by CT-guided 3D high-dose-rate(HDR)brachytherapy(BT)using a tandem and interstitial applicators,according to standard clinical practice in our hospital.At the beginning,a CT simulation was performed.The slice thickness of CT scans was 5 mm without an inter-slice gap,and images were sent to the treatment planning system(TPS).For IMRT TPS,we used Varian EclipseTM v10.0(Varian Medical Systems,Inc.Palo Alto,California,USA)for the contouring and planning process.The Clinical Target Volume(CTV)was composed of cervix,uterus,adnexaes,the upper half vagina,and pelvic lymph nodes.Planning Target Volume(PTV)was defined by CTV plus 0.5-1.5cm margin.For PTV,the D95(minimum dose covering 95%of the volume)of 1.8Gy per fraction,five fractions per week was prescribed to the total dose of 45 Gy.Four fractions of HDR brachytherapy with iridium-192 radioisotope were designed for all patients.Brachytherapy was carried out once a week,and first brachytherapy application was assigned to be performed after the 2th week of EBRT.EBRT was interrupted for each day of HDR brachytherapy insertion.Patients underwent a CT simulation for treatment planning in supine position.CT-images were acquired after the applicator was inserted.For all patients,the High-risk clinical target volume(HR-CTV)was contoured according to the CTstandardized contour guidelines:the whole cervix and the presumed extra-cervical tumor extension at the time of brachytherapy.Treatment plans were generated in the treatment planning system(Oncentra(R)Brachy v4.1,Nucletron B.V.,The Netherlands).For HR-CTV,the D90(minimum dose covering 90%of the volume)of HR-CTV in all patients was at least 7Gy × 4 fractions.The goal of IMRT and BT was the D90 of HR-CTV with EQD2>80Gy for patients with either a complete response or a partial response with residual disease less then 4 cm.For nonresponders or those with tumors larger than 4 cm at the time of brachytherapy,the D90 was an EQD2 of 85-90Gy.The BT planning CT images were imported into Varian EclipseTM to locate HR-CTV contour in the EBRT planning CT images.The image sets for BT planning were registered on the image set for EBRT planning of the same patient.To indicate the change among HRCTVs,HR-CTVs for the same patient were compared,and the HDI(HR-CTV deformation index)was defined as ratio of the common volume of four HR-CTVs for four brachytherapy insertions of the same patient with the total volume of the HR-CTV for one brachytherapy insertion of the patient.To indicate the nonoverlapping volume between HR-CTV and PTV,the NPI(nonoverlapping PTV index)was defined as ratio of the volume difference between HR-CTV and HR-CTV covered by PTV with the total volume of HR-CTV.To indicate the HRCTV cumulative dose relative to the EBRT PTV prescribed dose,the RPD(relative PTV dose)was defined as ratio of EBRT D95 difference between HR-CTV and PTV with the EBRT D95 of PTV.Results:A total of 22 EBRT plans and 88 brachytherapy plans were analysed.The means of HDI,NPI and RPD were 0.45±0.13,0.05±0.13,and-0.02±0.13,respectively.The numbers of BT plans with RPD>0,RPD=0,and RPD<0 were 50,8,and 30,respectively.The percentage of the above three cases were 56.8%(50/88),9.1%(8/88),and 34.1%(30/88),respectively.Conclusion:HR-CTV varied greatly during brachy treatments,but basically was within EBRT PTV.In most cases,the cumulative EBRT dose of HR-CTV was not equal to the EBRT PTV prescribed dose.In calculating the cumulative dose of the radiotherapy patient,the specific analysis of each case should be performed.