Exploring Factors Influencing CT Value Changes Of Tumor And Organs At Risk In Patients With Oropharyngeal Carcinoma During Adaptive Radiotherapy

Objective:Adaptive radiotherapy(ART)can modify the field and dose of radiation to achieve personalized treatment through feedback information during the course.The CT values of tumors and some normal tissues may change after radiotherapy.Such changes may be caused by local control of tumors or damage caused by radiotherapy.The shrinkage of tumor tissue and normal tissue damage caused by radiation can cause changes in CT values of tumor target areas and Organs at Risk,but the specific mechanism and influencing factors have not been clarified.The purpose of this article is to study the influencing factors of CT value changes of tumors and organs in patients with oropharyngeal carcinoma during adaptive radiotherapy.Methods:Seventeen patients with oropharyngeal cancer who underwent radical radiotherapy in our department from October 2017 to October 2018 were selected.All patients were diagnosed pathologically and received IGRT calibration.MIM fusion was used to calculate each tumor and OAR volume,dose,and average CT value.All data were entered into an Excel table.Regression statistical analysis was performed using SAS 9.4.A mixed linear model was used to analyze the influencing factors of tumor CT value,ipsilateral parotid gland CT value,contralateral parotid gland CT value and spinal cord CT value.Graph Pad Prism(Graph Pad software Inc,version 7.0)was used to perform Pearson correlation analysis between the volume and CT value changing rate of GTV,ipsilateral and contralateral parotid gland.Results:During the radiotherapy,the GTV,ipsilateral and contralateral parotid gland volume changes in the 17 oropharyngeal cancer patients were(0.39-40.78)cm~3,(0.74-12.91)cm3,and(1.48-14.73)cm3.The tumor volume of most patients(88%)was reduced,and the CT values of tumors and OARs(except for a few individual patients)were also reduced in most patients.However,there was no significant change in the volume or CT value of spinal cord.A linear mixed model analysis of relevant influencing factors found that tumor volume(?=1.2853,P<0.0001),age(?=11.22,P<0.0001),and stage(?=228.48,P=0.0363)were the influencing factors of the GTV CT value;ipsilateral parotid volume(?=0.4197,P<0.0001)and mean dose of the ipsilateral parotid gland dosage(?=-0.216,P<0.0001)were the influencing factors of the ipsilateral parotid CT value;volume of contralateral parotid gland(?=0.5612,P<0.0001)and gender(?=26.9063,P=0.0415)were the influencing factors of contralateral parotid gland CT value;5%volume of spinal cord dose(?=0.6071,P<0.0001),the average spinal cord dose(?=-0.7817,P<0.0001),and the spinal cord volume(?=0.4164,P=0.0021)were the influencing factors of the average CT value of the spinal cord.Pearson correlation analysis showed that the GTV volume change rate and CT value change rate were significantly correlated(r=0.6418,P=0.0055),and the ipsilateral or contralateral parotid gland volume change rate and CT value change rate were not significantly correlated.Conclusion:CT values of tumors and organs at risk of patients with oropharyngeal carcinoma decrease during radiotherapy.Age,tumor stage,and tumor volume are the main influencing factors.The CT value of each OARs was related to its volume,radiation dose,age and gender.Influencing factors vary among different OARs.