Analysis Of Dosimetry And Clinical Efficacy Of Pelvic Bone Marrow-sparing Intensity-modulated Radiotherapy In Advanced Cervical Cancer

Objectve:To compare the dosimetric difference on target-volume coverage and organs at risk(OAR) in pelvic bone marrow-sparing intensity-modulated radiotherapy(PBMS-IMRT) with intensity-modulated radiotherapy(IMRT) in the treatment of advanced cervical cancer,to observe the recent clinical efficacy and acute toxicity both PBMS-IMRT and IMRT combined with chemotherapy,and to explore the feasibility of clinical application of PBMS-IMRT.Methods:From March 2013 to June 2013,20 consecutive cervical cancer patients,with stageⅡb-Ⅲb, were evaluated for dosimetry study.And 120 patients,from July 2013 to June 2014,were randomly divided into two groups(PBMS-IMRT 60 and IMRT 60) for clinical study.A CT scan of each patient was obtained.The clinical target volume(CTV) was contoured.CTV included GTV,cervix uteri,corpus,fundus,vagina,parametrial tissue and pelvic lymph nodes.The margins of planning target volume(PTV) were generated based on CTV margins by which added 1.0cm extension in superior and downward,0.5 cm in forward and backward,0.7 cm in all other dirctions.OARs included bladder,bowel,rectum and pelvic bones(which comprised the haunch bone, sacral bone,proximal femora,femoral heads and part of lumbosacral bone).The dose-volume constraints of OARS:bowel V30 <40%,bladder and rectum V40 <40%,V50 <20%.The pelvic bones’ dose-volume constraints of PBMS-IMRT were V20 <75%,V40 <37%,Dmean <34Gy.PBMS-IMRT and IMRT were designed.All plans were designed using 7 field coplanar and 6MV X photon.The prescribed dose to the PTV was 45 Gy ~ 50.4Gy(50.4Gy for dosimetry study),1.8Gy per fraction,5 fractions per week.And 95% of the planning target volume received the prescribed dose.Three or four weeks later,high dose rate brachytherapy of 24 Gy ~ 30 Gy to point A were followed,once a week with 6 ~7Gy/fraction and 4-5 times.Each patient received concurrent oxaliplatin 130mg/m2*d1 and tegafur 800 mg ~1000mg/d*d1-d5 per four weeks.SPSS13.0 software package was applied for analysing dose-volume histogram(DVH),homogeneity index(HI),conformity index(CI),OAR does and volume parameters,recent clinical efficacy and acute toxicity.Results:Dosimetry:PBMS-IMRT, with adequate coverage and the same HI(P=0.841>0.05), had an advantage over IMRT in term of CI(P=0.000 <0.05). PBMS-IMRT had an obvious reduction of the irradiated volume of pelvic bone marrow at10~50Gy(P <0.000). Furthermore, PBMS-IMRT was superior to IMRT in reducing the does to small bowel at 10 Gy,20Gy(P=0.001、P=0.000 <0.05). No statistically significant differences were observed between two plans’ irradiated volume of bladder and rectum. Clinical Efficacy:The recent clinical effective rate in PBMS-IMRT was 97%,which in IMRT was 95%(χ2=0.570 P=0.903 >0.05).The rate of acute hematopoietic toxicity in PBMS-IMRT was 30%,53%was in IMRT(χ2=6.720 P=0.01 <0.05).And the incidence of acute gastrointestinnal toxicity was 28% in PBMS-IMRT,which was 26% in IMRT(χ2=0.042 P=0.838 >0.05);the rate of acute genitourinary toxicity was 13% in PBMS-IMRT and 11% in IMRT(χ2=0.076 P=0.783 >0.05).Conclusion:PBMS-IMRT could be to reduce the pelvic bone marrow volume irradiated at all does levels in dosimetry.And two plans had the same clinical efficacy. PBMS-IMRT could be lower the acute hematopoietic toxicity, decreasing the delay rate and interruption rate of radiation therapy and improving the quality of life.