The Influence Of Bladder State On Target Tumor And Organs At Risk In Intensity-Modulated Radiotherapy For Cervical Cancer

[Objective] The aim of this study was to compare the displacement of PTV、cervix and surface reference points and the differences of irradiated volume percentage of CTV、PTV、bladder、small bowel、rectum and femur heads between full bladder and empty bladder in intensity-modulated radiotherapy (IMRT) for cervical cancer using prone position.[Methods] 21 patients diagnosed with cervical cancer in stage IIB-IIIB were aquired between December 2014 and October 2015 in the Third Affiliated Hospital of Kunming Medical University.IMRT treatment plans were conducted respectively on full and empty bladder CT scanning images using the prone position.Then collect data to compare between full and empty bladder filling and emptying:(1)the conformity index (CI)、uniformity index (UI)、D5、D50 and D95 differences of PTV;(2) the three dimensional displacement of PTV,cervix and surface reference points(REF); (3) the change of percentage of irradiated volume of CTV、PTV、bladder、small bowel、 rectum and femur heads.[Results](1) The mean volume of filling and empty bladder were (420.5±166.52) ml and (99.7±63.22) ml respectively(P<0.001).(2) The conformity index (CI) and uniformity index (UI), D5,D50, D95 of PTV had no significant differences between IMRT plans on full bladder and empty bladder(P>0.05). (3)The displacement in Y axis(direction of Anteriorly/Posteriorly)of PTV and cervix were (0.2+0.2) cm and (0.8+1.06) cm respectively from full bladder to empty(P<0.05),while there were no significant displacement in X axis(direction of Right/Left) and Z axis(direction of Superiorly/Inferior).The displacement of surface reference points(REF) were not obvious in all direction (P>0.05).(4)The volume of CTV、PTV and small bowel, rectum, and femoral head has no differences between two bladder status (P>0.05).(5) The mean radiation dose(Dmean) of small bowel in the state of bladder filling were significantly lower than those in the state of emptying(P<0.05),while the mean radiation dose(Dmean) of rectum in full bladder were higher(P<0.05). No obvious differences of the mean radiation dose(Dmean) of CTV, PTV and bladder, femoral head were showed in two bladder status.(6)The percentage of irradiated volume of small bowel were lower in plan on full bladder than plan on empty bladder(P<0.001),while the irradiation volume percentage received 45Gy(V45) of rectum were higher in plan on full bladder(P=0.023),with no differences of V5-V40 (P>0.05).The percentage of irradiated volume of CTV, PTV and bladder, femoral heads showed no significant differences in plans on full bladder and empty (P>0.05).(7)Analysis of subgroup with pelvic or para-aortic lymph node metastasis indicated that with full bladder,the V45 of small bowel were lower (P<0.05) while V45 of rectum elevated (P<0.05).In subgroup without lymph node metastasis,the V45 of small bowel and bladder were lower with full bladder(P<0.05),and no differences were showed in V45 of rectum(P>0.05).[Conclusions] (1)There were significant displacement of PTV and cervix in Y axis (direction of Anteriorly/Posteriorly) from full bladder to empty.(2)Pelvic radiation in patients with cervical cancer in stage IIB-IIIB,with full bladder,using IMRT and prone position,could reduce the irradiation volume percentage of intestine.(3)Keeping a filling bladder may increase the irradiation volume percentage of rectum while reduce the intestine’s in pelvic radiation using IMRT and prone position for patients with pelvic or para-aortic lymph node metastasis.