Dpsimetry Analysis Of IMRT And VMAT In Locally Advanced Middle And Lower Thoracic Esophageal Carcubina

ObjectiveTo compare the differences of dosimetry and planning complexity between intensity-modulated radiation therapy(IMRT)and volume modulated arc therapy(VMAT).We will explore the dosimetric advantages and characteristics of these two radiotherapy technologies,so as to provide a reference for clinical patients with esophageal cancer to choose a more appropriate radiotherapy scheme.MethodsFrom 2017 to 2018,20 patients with locally advanced middle and lower thoracic esophageal cancer who received radiotherapy in our hospital were selected.The median age of the patients was 58 years old,and the ratio of male to female was 3 to 2.Prepare for each patient before radiotherapy,including fixing body position,scanning CT,etc.Combined with the patient’s auxiliary examination,the target area and normal tissue were delineated.The target area includes tumor target volume(GTV)and clinical target volume(CTV).At the same time,the normal tissues include lung,heart and spinal cord.On this basis,the normal tissues in the lower thoracic esophageal cancer also include liver and stomach.We designed IMRT and VMAT radiotherapy plans for each patient.The prescription dose of PGTV was 60Gy/30f;PTV was 54Gy/30f.In the planning system,the dose volume histogram(DVH)and isodose curve are used to obtain the dosimetric parameters of the plan,including the maximum dose(Dmax),the minimum dose(Dmin),the average dose(Dmean),the conformal index(CI),the homogeneity index(HI)and so on.In addition,obtain the plan complexity parameters through scripts.Finally,SPSS software was used to compare the differences between the two radiotherapy plans.Results1.There was no significant difference in the Dmean,Dmin,Dmax and D99 of the two radiotherapy plans for PGTV and PTV,no matter in the middle or lower thoracic esophageal cancer.Among patients with mid-thoracic esophageal cancer,the D95 of PTV in IMRT plan was higher than that in VMAT plan,and the difference was statistically significant(P=0.047).In patients with lower esophageal cancer,there was no significant difference between the two plans(P=0.575).In terms of conformal index(CI),both PGTV and PTV of VMAT plan were better than IMRT,only in the PGTV of patients with middle thoracic esophageal cancer,the difference between the two was not significant,and the rest were significant.There was no significant difference between the two radiotherapy plans in the homogeneity index(HI),no matter in the middle or lower thoracic esophageal cancer.2.For the lungs of organs at risk,there was no significant difference in Dmean between the two plans,but V5 and V10 of VMAT plan were significantly higher than that of IMRT plan(P<0.05),while V20 and V30 of VMAT plan were lower than that of IMRT plan,and the difference was significant(P<0.05).In terms of heart,V10 of VMAT plan was significantly higher than that of IMRT(P<0.05).For Dmax of the spinal cord and Dmean,V30,V40 and V50 of the heart,there was no significant difference between IMRT and VMAT in middle or lower segment cases.The differences of Dmax,V30,V40 and V50 in the stomach also were not significant.For the liver,the Dmean,V20,V30 and V40 of VMAT plan were slightly higher than that of IMRT,but the difference was not significant.3.Compared with IMRT,VMAT can significantly reduce monitoring units(MU).For middle esophageal cancer,VMAT’s MU can reduce 12.7%on average compared with IMRT,and for lower esophageal cancer,it can reduce 13.8%.In terms of complexity,the MU/CP value of VMAT was significantly higher than that of IMRT in both middle and lower segments.Conclusion1.VMAT and IMRT plans are comparable in dose coverage and homogeneity index of PGTV and PTV.In terms of conformal index,VMAT plan is obviously superior to IMRT.2.For lung protection,VMAT significantly reduced the volume of high-dose exposure(V20,V30),but also increased the volume of low-dose exposure(V5,V10).For the heart,VMAT also significantly increased low-dose exposure.For the protection of spinal cord,stomach and liver,the two plans are equivalent.3.The delivery efficiency of VMAT is higher than that of IMRT,and the complexity of VMAT is greatly reduced.