The effect of contrast agents on the planned dose of VMAT radiotherapy for upper esophageal cancer
Objective To explore the impact of residual contrast agent in the brachial vein to superior vena cava on VMAT radiotherapy dose planning for upper esophageal cancer.Methods Ten patients with upper esophageal cancer were selected.Contrast agent was intravenously injected during positioning,and CT simulation scans were performed.The images were transferred to the Varian Eclipse 11.0 planning system.The CT values of the contrast-enhanced vessels were measured and then converted to 40HU using a assigning method.VMAT plan 1 was created on the enhanced CT,and then the CT values of the major vessels from the axillary vein to the superior vena cava were assigned and corrected on the enhanced CT to create VMAT plan 2.The D2 and D98 of the target area PGTV and PTV,conformity index(CI),homogeneity index(HI),as well as the dose distribution of normal organs such as lung,spinal cord,and humeral heads were calculated before and after assignment,and the effects of the two plans on the number of accelerator treatments(MU)were compared.The impact of high CT values caused by contrast agent injection on the dose of target area and organs at risk was assessed using rank sum test.Results There were statistically significant differences in D2 of PTV and D98 of PGTV(P<0.05).However,there were no statistically significant differences in D98 of PTV and D2 of PGTV(P>0.05).There were no statistically significant differences in conformity index(CI)and homogeneity index(HI)(P>0.05).Statistically significant differences were observed in V5 and V10 of lung,as well as the average dose of the left and right humeral heads(P<0.05),but no statistically significant differences were found in V20 and V30 of the lung(P>0.05).The number of accelerator treatments(MU)in both plans showed statistically significant differences(P<0.05).Conclusion Residual contrast agent from the brachial vein to the superior vena cava has a certain impact on the target area dose of VMAT planning for upper esophageal cancer,but the impact is within an acceptable range.Contrast agent increases the low-dose regions V5 and V10 of the lung and increases the average dose of humeral heads.Additionally,the contrast agent leads to an increase in the number of accelerator treatments(MU).
Esophageal cancerRadiotherapyContrast agentCT valueConformity index
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