Dosimetric Comparison Between IMRT And VMAT For Different Lesion Length Of Upper Esophageal Cancer

Objective:To compare the dosimetry difference between static intensity-modulated and volumetric –modulated arc therapy on the upper esophageal cancer,at the same time compare the dosimetry difference of IMRT and VMAT on different length of tumors of the upper esophageal cancer,explore whether according to the length of the esophageal lesions on CT to choose the right means of radiation therapy.Method:Selecting 20 patients of upper thoracic esophageal cancer who were placed in a department in Jiangxi tumor hospital from June 2013 to June 2017.According to the classification of esophageal tumor length measured on CT,10 cases <5cm and5-9cm10 cases were divided into 5F-IMRT and double arc VMAT radiotherapy plans.All the target area are the same prescribed dose,PTV-GTV 6000cGy/27F/6W,PTV-CTV 5000cGy/27F/6W.The relative dose parameters of two radiotherapy regimens for total esophageal cancer and tumor grouping were compared.Results:In the dosimetric comparison of two plans for PTV60 in 20 patients with esophageal cancer,VMAT's target areas CI and HI(p<0.001)were superior to IMRT.In different tumors had the length of the target dose comparison,two groups of VMAT CI and HI are better than that of IMRT,IMRT in GTV length: 5-9 cm group compared with the length of GTV < 5 cm of CI and HI all decline trend,but the VMAT not present a downward trend.In the dosimetry comparison between the two plans,the lung V5 value of IMRT was lower than VMAT(p=0.021),while the lung V10,V15,V20,V30,V40 and MLD,the spinal cord Dmax and the posterior tracheal wall Dmax were dominant(p <0.001).Among the groups with different tumor length,VMAT value of lung V5 in both groups was higher than that of IMRT,but there was no significant difference in lung V5 in GTV<5cm group(p=0.38).In GTV length: 5-9cm group VMAT lung V5 is higher than in IMRT,V10 two plans have no obvious differences(p = 0.196),the other two groups VMAT in V15,V20,V30,MLD,spinalcord Dmax and tracheal Dmax are superior to IMRT(p < 0.05).In 20 patients with esophageal cancer,the number of machine jumps of IMRT was higher than VMAT(p=0.001).In the two groups of esophageal lesions,the number of monitor unite of IMRT was higher than that of VMAT(<5cm,p=0.014).5--9 cm,p = 0.022).Conclusion:(1)Compared with the target dose distribution between IMRT and VMAT for tumors length < 5 cm of the upper esophageal cancer,VMAT has obvious advantages;(2)For the tumors 5-9 cm length of upper esophageal cancer,VMAT still has the relative advantage than IMRT,although VMAT lung V5 higher than that of IMRT,but VMAT V5 is still within the acceptable range,V20,MLD are lower than that of IMRT,and spinal cord,tracheal protection and reduce the MUs is better than that of IMRT.Therefore,VMAT has certain advantages over IMRT in radiotherapy of upper esophageal carcinoma.