Fusion Dose Comparison Of External Beam Radiotherapy Combined With Intracavitary Brachytherapy Under Different Bladder Status For Locally Advanced Cervical Cancer

Objective: Cervical cancer is one of the common malignant tumors in women,According to the FIGO stage,the patients before stage IIa can be treated with surgery,and the patients with stage after IIb should mainly be treated with radiotherapy.Radiotherapy for cervical cancer includes external beam radiotherapy(EBRT)and intracavitary brachytherapy(ICBT),EBRT combined with ICBT is a standard radiotherapy technology for locally advanced cervical cancer(LACC),bladder status is a common factor that affects dose distribution of target and organs at risk(OARs).For a long time,dose evaluation of the targets and OARs for LACC in EBRT and ICBT radiotherapy were completed in the corresponding plan,lack of fusion dose evaluation,Therefore,it is not clear how the dose distribution in EBRT /ICBT fusion plans under different bladder status for LACC.The main purpose of this study is to compare geometry and fusion dose distribution of the targets and OARs between BOX-RT/ICBT plans and IMRT/ICBT plans by Oncentra TPS(treatment planning system)under different bladder status.Methods: Total 20 patients with LACC treated in our department from 01,01,2015 ~ 31,07,2015 were undergone magnetic resonance imaging,(MRI)and simulation computed tomography(Sim-CT)scan respectively under empty and filling bladder,transmitted Sim-CT to oncentra treatment planning system(TPS),and fused MRI and Sim-CT.Delineated the gross tumor volume(GTV)in MRI,clinical target volume(CTV),planning target volume(PTV)and OARs(intestine,bladder,rectum,left and right femoral head)in SimCT.Designed IMRT/ICBT plan and BOX-RT/ICBT plan in TPS,radiation sources as 6MV-x-ray and 192 Ir respectively.Alone calculated doses of targets(D95%,D90%,D85%,D80%)and OARs(D1cc、2cc for intestine,D5%、10%、30% for bladder,D1cc、2cc、5cc for rectum,D1% for femoral head)with EBRT(IMRT and BOX-RT)and ICBT separately,and geometric sum as geometric dose.Used TPS plan superposition function,superimposed EBRT and ICBT plans as a fusion plan,and calculated doses of targets and OARs as fusion dose.Analysing the relationship between geometric and fusion doses of targets and OARs under different bladder status,and calculated the dose contribution rates to targets and OARs from ICBT.To compare geometry and fusion dose of the target and OARs under two kinds of EBRT.The data conform to the normal distribution by the paired t test,or the signed rank sum test is used.The statistic of the parameter test is set to t,the non-parametric test statistic is set to u,and the test level is α=0.05.Results:1.BOX-RT/ICBT plan: For empty bladder,D95%(uGTV=3.92,tCTV=14.59,tPTV=14.76)、 D90%(uGTV=3.92,tCTV=16.51,tPTV= 16.86)、 D85%(uGTV=3.92,tCTV=18.24,tPTV=19.54)、 D80%(uGTV=3.92,tCTV= 16.04,tPTV=17.98),The geometric doses of targets were lower than the fusion doses;For full bladder D95%(uGTV=3.92,tCTV=11.88,tPTV= 12.01),D90%(uGTV=3.92,tCTV=13.80,tPTV=13.71),D85%(uGTV=3.92,tCTV= 16.26,tPTV= 17.06),D80%(tGTV=17.50,tCTV=16.68,tPTV=18.46),The geometric doses of targets(D95%,D90%,D85%,D80%)were lower than the fusion doses;P<0.001.geometry and fusion dose difference of GTV,CTV and PTV was similar,GTV dose difference rate is less than 5%,CTV and PTV more than 5%.The geometric dose of the OARs were higher than fusion dose,geometric and fusion dose difference rates of small intestine and rectum are most obvious,more than 5%;geometric and fusion dose difference rates of bladder and femoral head were similar,less than 5%.Under the filling bladder,fusion dose of OARs are minimum.In different bladder status,the geometric dose contribution rate of the ICBT to the targets was lower than the fusion dose contribution rate,more than 3%.Difference between geometry and fusion dose contribution rate of ICBT to the target is similar,that the highest geometry and fusion dose contribution rate are for GTV,more than 49%.The smaller geometry dose contribution rate to the CTV 、 PTV,less than 10%.but the contribution rate of fusion dose was higher than that of geometric dose.For the empty and filling bladder status,geometric dose contribution rate of ICBT to OARs were higher than the fusion dose contribution rate,geometric and fusion dose contribution rate difference of small intestine and rectum was more than 6%,dose difference of bladder and femoral head was similar.In empty bladder,the geometric and fusion dose contribution rate of ICBT to OARs is higher than the filling bladder.Under the filling bladder,fusion dose contribution rate to OARs is minimum.2.IMRT/ICBT plan: For empty bladder,D95%(uGTV=3.92,tCTV=11.28,tPTV=10.79),D90%(uGTV,CTV=3.92,uPTV=3.25),D85%(u=3.92),D80%(u=3.92),The geometric doses of targets were lower than the fusion doses;For full bladder D95%(uGTV,PTV=3.92,tCTV=15.96),D90%(uGTV=3.81,uCTV,PTV=3.92),D85%(u=3.92)、 D80%(uGTV= 4.70,uCTV,PTV=3.92),The geometric doses of targets(D95%,D90%,D85%,D80%)were lower than the fusion doses;.P<0.001.Dose difference rate of GTV under filling bladder was lower than empty bladder(0.17%~0.93% and 0.32-1.07% respectively),while that were similar with empty bladder for CTV and PTV(1.10%~2.75% and1.22%~3.40%,0.98%~2.29% and 0.94%~3.17% respectively).For empty bladder,the geometric doses of OARs(uintestine=3.92,tintestine=11.59;ubladder=3.92,3.92,3.36;urectum =3.92;tfemoral head = 4.77 and 6.06)were higher than the fusion doses;For full bladder,the geometric doses of OARs(tintestine=10.27,8.84;tbladder=10.69,11.77,4.91;urectum=3.36,3.21,3.25)were higher than the fusion doses,P<0.005.The average geometric dose differences of D30% for bladder and D1 cc,2cc,5cc for rectum were higher than that of fusion(1.90 Gy,1.01 Gy,0.87 Gy,0.86 Gy and 1.86 Gy,0.95 Gy,0.79 Gy,0.59 Gy respectively).D1% for right and left femoral head were 0.76Gy、0.41 Gy and 026Gy、0.73 Gy.For empty bladder,D95%(uGTV=3.92,tCTV=11.40,tPTV=10.84),D90%(uGTV=3.92,uCTV=3.29,tPTV=6.00),D85%(uGTV=3.92,tCTV=17.29,tPTV=13.87),D80%(uGTV=3.92,tCTV=16.60,tPTV=15.41),geometric dose contribution rate to targets was lower than fusion dose contribution rate from ICBT;For full bladder,D95%(uGTV=9.87,uCTV=15.78,uPTV=10.65),D90%(uGTV= 3.81,tCTV=20.70,tPTV=17.64),D85%(tGTV=8.31,tCTV=23.27,tPTV=19.78),D80%(tGTV=4.68,uCTV=3.92,tPTV=19.90),geometric dose contribution rate to targets was lower than fusion dose contribution rate from ICBT;P<0.05.The highest dose contribution rate was GTV,geometric and fusion contribution rates were 51.12% ~ 63.89% 、 48.10% ~ 60.80% and 49.52% ~ 63.35% 、 46.74% ~60.52% under empty and filling bladder respectively,while it was less than 10.00% for CTV and PTV.For empty bladder,geometric dose contribution rate to OARs(uintestine=3.92;ubladder=3.92,3.92,3.36;urectum=3.92;tfemoral head=4.67 and 6.16)was higher than fusion dose contribution rate from ICBT;For filling bladder,geometric dose contribution rate to OARs(tintestine=10.14,8.77;tbladder=10.74,11.82,4.93;urectum=3.25,3.21,3.21)was higher than fusion dose contribution rate from ICBT;P<0.005.Dose contribution rates from ICBT to rectum were 47.77% ~ 59.45% and 40.87% ~ 52.40%,47.82% ~58.78% and 41.61%~52.00% respectively,27.60%~45.17% and 26.04%~41.80%,23.36%~43.67% and 21.89%~40.22% to bladder,30.90%~36.90% and 28.85% ~ 34.79%,20.68% ~ 25.13% and 18.69% ~ 22.88% to intestine,less than 10% to right and left femoral head compared empty bladder with filling bladder.3.BOX-RT/ICBT and IMRT /ICBT plan: For the empty bladder,dose difference between the BOX-RT/ICBT plan and IMRT /ICBT plan in PTV(D95%,D80%)was statistically significant.Dose of IMRT /ICBT plan is higher than that of BOX-RT/ICBT plan in PTV D95%,dose difference value was 3.26 ± 1.32Gy;BOX-RT/ICBT plan dose is higher than the IMRT /ICBT plan dose in PTVD80%,dose difference value was 1.52 ±1.25 Gy.For filling bladder,dose difference between the BOX-RT/ICBT plan and IMRT /ICBT plan in CTV(D95%,D80%),PTV(D95%,D80%)was statistically significant.IMRT /ICBT plan dose is higher than BOX-RT/ICBT plan dose in CTVD95% and PTVD95%,different dose values were 1.49 Gy,1.51Gy;BOX-RT/ICBT plan dose is higher than the IMRT /ICBT plan dose in CTVD80% and PTVD80%,dose differences were 0.95 Gy,1.04 Gy.Under different conditions of bladder,for small intestine and rectum,dose value of BOX-RT/ICBT plan was significantly higher than that of IMRT /ICBT plan,the difference was statistically significant(P<0.05).Especially in the rectum,the dose difference values were >5Gy.In filling bladder,dose value of BOX-RT/ICBT plan for small intestine was higher than that of IMRT/ICBT plan,dose difference value were >2Gy.What the bladder status is,in BOX-RT/ICBT fusion plan,dose contribution rate of ICBT to the target was significantly higher than that of IMRT/ICBT fusion plan,(P<0.05),the difference of dose contribution rate to GTV were >5%,dose difference contribution rate to CTV,PTV were >4%.In BOX-RT/ICBT fusion plan,dose contribution rate of ICBT to the OARs was significantly lower than that of IMRT/ICBT fusion plan,(P<0.05),the difference of dose contribution rate to the intestine was >5%,to the rectum was >7%.Conclusions : 1.For locally advanced cervical cancer,the fusion evaluation of external irradiation(BOX-RT and IMRT)in combination with ICBT is better than pure geometry evaluation,The dose difference between geometry and fusion dose was greatest in the rectum,but further clinical observation is needed.2.bladder status can affect the dose of the targets and OARs,calculating the targets and OARs dose of simple geometry has a certain limitations,the best is fusion dosimetric analysis.3.In the course of radiotherapy of cervical cancer,bladder filling is conducive to the protection of OARs,especially in the small intestine and bladder,suggest that the external irradiation combined with ICBT,the bladder should maintain a certain capacity.Although the bladder filling reduced dose of the OARs,further clinical study need to be done.4.Compared with simple external irradiation(BOX-RT or IMRT),ICBT has significant advantages,especially combined with four field BOX-RT,the advantage of ICBT is more obvious.Compared with the four field BOX-RT,IMRT can increase the dose of the targets in precision and reduce the exposure doses of OARs.