Dosimetric Research On Imrt With Simultaneous Integrated Boost And Conventional Sequential Boost To The Parametrium For Cervical Cancer

Objective:To compare the dose distributions of intensity-modulated radiotherapy using the simultaneous integrated boost(IMRT-SIB)technique with that of the traditional midline block(IMRT-MB)technique for boosting the parametrium in patients with cervical cancer.To determine a more appropriate way of radiotherapy for cervical cancer with parametrial extension.Materials and methods:A total of 10 patients with locally advanced cervical cancer treated in our hospital were analyzed.All patients were in clinical stage ?B,and imaging confirmed no distant metastasis.The patients were scanned by CT simulation and their target volumes and organs at risk(OARs)were delineated.Treatment plans IMRT-SIB and IMRT-MB were generated for each of the 10 patients by the same physicist.For the IMRT-SIB plans,45 Gy and 54 Gy dose levels in 25 equal fractions were set for the pelvis planning target volume 45(PTV45)and the parametrial boost volume(PTV54),respectively.For the IMRT-MB plans,the parametrium was sequentially boosted with the MB technique(9Gy in five fractions)after pelvic IMRT(45Gy).The dose constraints of OARs: rectum V50<35%,bladder V50<50%,bowel V45<250cc,femoral heads V50<5%.Dose parameters of target volumes and OARs of both plans were evaluated.Statistical analysis of SPSS26.0 system was used to compare the differences between the two techniques.Results:The maximum dose(Dmax)and mean dose(Dmean)of the PTV54 were higher for IMRT-SIB plan than those for IMRT-MB plan(P<0.001,P<0.001).But the Dmean and the volume receiving 100% of the prescribed dose or more coverage(V100)of the PTV45 were lower for IMRT-SIB plan than those for IMRT-MB plan(P=0.009,P<0.001).The PTV45 and PTV54 conformal index(CI)of IMRT-SIB plan were 0.89±0.01 and 0.86±0.03 respectively,and those of IMRT-MB plan were 0.87±0.01 and 0.45±0.05 respectively.The CI of the IMRT-SIB plan were significantly better than that of the IMRT-MB plan(P<0.001,P<0.001).The constraints were met for all of the OARs in both two groups.Compared with IMRT-MB,the IMRT-SIB technique significantly reduced the volume receiving 50 Gy or more(V50)for the rectal,the volume receiving 20 Gy or more(V20),the volume receiving 30 Gy or more(V30),the volume receiving 40 Gy or more(V40)and V50 for the bladder,and the volume receiving 10 Gy or more(V10),V20,V40,V50 and Dmean for the bowl.Regarding the femoral head,the V10,V30 and Dmean for the left femoral head,and the V30 and Dmean for the right femoral head of IMRT-SIB plan were higher than IMRT-MB plan,and the differences between two plans were statistically significant(P=0.007,P=0.005,P=0.005,P=0.001,P=0.002).But both groups were much lower than the dose constraints.Conclusions:1.As compared with IMRT-MB plan,IMRT-SIB plan achieved better CI,and its dose distribution was closed to target volume.2.As compared with IMRT-MB plan,IMRT-SIB plan received lower dose to the rectum,bladder and bowl,and showed the advantages in the protection of OARs.3.As compared with IMRT-MB plan,IMRT-SIB plan increased biologically effective dose and shortened the overall treatment time.