Relationship Between Volume And Dose Of Tumor Target And Organs At Risk In CT Image-based Cervical Cancer Brachytherapy

Purpose:The current brachytherapy of cervical cancer has entered the three-dimensional era,its local control rate and overall survival rate have been improved,but there are also some complications.The incidence of complications such as radioactive enteritis and radioactive cystitis is related to the dose of radiation.In recent years,the relationship between the volume and dose of organs at risk has been different.The aim of this study was to investigate the relationship between the volume of high-risk clinical target,organs at risk(bladder,rectum,and sigmoid colon)and the dose in CT image-based 192Ir high-dose-rate brachytherapy of cervical cancer.Method:From January 2016 to February 2017,45 patients with cervical cancer admitted to the Department of Oncology of Guangzhou First People's Hospital were collected.All patients received external beam radiotherapy of three-dimensional conformal radiotherapy or intensity-modulated radiotherapy.The prescription dose was 45-50 Gy,and the routine segmentation was 1.8-2.0 Gy,which was performed 25 times in total and5 times a week.One week after the completion of external beam radiotherapy,CT-guided192Ir high-dose-rate brachytherapy was started.The prescription dose was 6 Gy each treatment.Each patient had brachytherapy 4 to 5 times and once a week.This study was followed brachytherapy a total of 218 times.Before each brachytherapy,CT positioning scans were performed to obtain images.The high risk clinical target volume(HR CTV)and organs at risk(OAR)bladder,rectum,and sigmoid colon were drawn by the same radiotherapy physician on the brachytherapy planning system.The dose volume histogram(DVH)was used to evaluate the volume and dose of the high risk clinical target volume and organs at risk bladder,rectum,and sigmoid respectively,and compared thedoseofdifferentvolumegroupsofhighriskclinicaltarget volume,bladder,rectum,sigmoid colon.In this study,high risk clinical target volume were divided into 3 groups by volume:HR CTV>120cm~3 group,80~120cm~3 group,and<80cm~3 group;analysis the difference of EQD2(equivalent dose in 2Gy fraction),D90(90%of the respective volume),V200(200%of the prescribed dose),V150(150%of the prescribed dose),V100(100%of the prescribed dose)in high risk clinical target volume.Bladder was divided into 3 groups according to volume:bladder volume>30cm~3 group,20-30cm~3 group,<20cm~3 group;analysis of differences between groups about EQD2,D2cc(Dose of 2cm~3),D1cc(Dose of 1cm~3),D0.1cc(Dose of 0.1cm~3).The rectum was divided into two groups according to volume,the rectum volume>15cm~3 group and?15cm~3 group;the differences of EQD2,D2cc,D1cc,D0.1cc between the two groups were analyzed.The sigmoid colon was divided into three groups according to the volume,that is the sigmoid colon volume>20cm~3 group,10~20cm~3 group,<10cm~3 group;the differences of sigmoid colon EQD2,D2cc,D1cc,D0.1cc between the three groups were analyzed.SPSS 19.0 software was used for statistical analysis.The observed dose is expressed as"mean±standard deviation"(?x±s).The t-test was used to compare the two groups of independent samples.The comparison between the three groups was analyzed by one-way ANOVA,and the two groups were compared using the SNK method.The difference was statistically significant at P<0.05.Results:1.The results of dose of high risk clinical target volume with different volume showed that compared with the high risk clinical target volume of>120cm3 and80~120cm3 group,the dose of D90 was increased,and the difference was statistically significant(P<0.05).That is,when the tumor target volume is smaller,the dose of D90 is higher.Compared with the high risk clinical target volume of 80~120cm3 group,the dose of V200,V150 in group of>120cm3 and<80cm3 is increased,the difference was statistically significant(P<0.05).Indicating that high dose volume of tumor target is increased.However,there was no significant difference of EQD2 and V100 in different groups(P>0.05).When the volume of the tumor target is different,there is no difference in the coverage of prescription dose and the equivalent biological dose of 2Gy fractionated radiotherapy.2.The dose of bladder with different volume showed that compared with the group of>30cm3 and 20~30cm3,the bladder dose of EQD2,D2cc,D1cc,and D0.1cc in<20cm3 group were all reduced,and the difference was statistically significant(P<0.05).There was no significant difference in the dose of EQD2,D2cc,D1cc,and D0.1cc between>30cm3 group and 20-30cm3 group(P>0.05).That is,when the volume of bladder is smaller,dose is lower.3.The dose of rectum with different volume showed that compared with the group of>15cm3,the rectum dose of EQD2,D2cc,D1cc,and D0.1cc in?15cm3 group were all reduced,and the difference was statistically significant(P<0.05).That is,when the rectum volume is smaller,the rectal wall is exposed to a lower dose.4.The results of dose of sigmoid colon with different volume showed that the dose of EQD2,D2cc,D1cc and D0.1cc in 10~20cm3 and 10cm3 groups gradually decreased with the volume decrease compared with the group of>20cm3,and the difference was statistically significant(P<0.05).That is,the smaller the volume of the sigmoid colon,the lower dose.Conclusion:1.In the three-dimensional brachytherapy of cervical cancer,when the volume of high risk clinical target is smaller,the HR CTV D90 is higher,and it can be understood that D90 can easily reach the prescribed dose.Therefore,in clinical work,for patients with small tumor size,three-tubes intracavitary brachytherapy can be reasonably selected based on the location of the tumor and the patient's wishes,thereby reducing the pain and the risk of bleeding during interstitial brachytherapy.When the HR CTV is>120cm~3or<80cm~3,the high-dose volume of the tumor target increases,which has a positive effect on the treatment of cervical cancer.2.When the bladder volume is smaller,the dose is lower.Considering that the bladder is relatively small,it is far from the high dose area,so that the dose is lower.In clinical work,it is recommended to empty the bladder before brachytherapy in order to reduce the dose of bladder wall.3.The rectal wall receives a lower dose when the rectum volume is smaller.Considering the non-uniform distribution of radiation dose in different parts of the rectum.Therefore,it is recommended that patients should empty the rectum before brachytherapy,in order to reduce the rectum volume,thereby reducing the dose of the rectal wall;and fully fill the vagina with gauze to increase the distance between the rectum and radioactive sources,is expected to reduce rectal wall dose.4.The dose of the sigmoid colon gradually decreased as the volume decreased.Considering that the dose of sigmoid colon in cervical cancer brachytherapy is related to the stepwise and non-uniform distribution.Therefore,reducing the volume of the sigmoid colon during the brachytherapy of cervical cancer is expected to reduce its dose.