Explore The Effect Of Parotid Dland Dose On The Incidence Of Xerostomia In Nasopharyngeal Carcinoma Patients-multicenter Retrospective Study

Objective: The purpose of this study was to explore the Nasopharyngeal carcinoma(NPC)after radiotherapy in patients with long-term side effects-xerostomia including its incidence and relationship with radiotherapy in parotid gland dose,and find out the parotid gland dose cut off value.The parotid gland dose was used to establish a prediction model,and the occurrence and grading of xerostomia were predicted by parotid gland dose during radiotherapy,providing theoretical basis for improving the long-term quality of life of patients with nasopharyngeal carcinoma.Methods: This study retrospectively analyzed 462 patients pathologically diagnosed with nasopharyngeal cancer from 2012 to Sichuan Provincial Cancer Hospital and Southern Hospital of Southern Medical University in 2017 and received radical radiotherapy without distant metastasis and recurrence.Patient’s highest xerostomia grade(HXG)and long-term xerostomia grading(LTG)symptoms were graded according to the common drug toxicity criteria and the radiation therapy oncology group(RTOG).Basic data of patients were collected from the medical record system and followed up through outpatient service and telephone.The mean dose(Dmean)and dose received at 50% volume(D50)were collected by the planning system and dose volume histogram(DVH).The receiver operating characteristic curve(ROC)and Yoden index in Medcalc software were used to find the cutoff of parotid dose.Kaplan-Meier univariate analysis was performed using SPSS software,multivariate analysis of the HXG by Logistic regression,and the COX regression model performed multivariate analysis of LTG to identify independent risk factors of xerostomia occurrence in NPC patients.At the same time,the patient’s gender,radiotherapy method,number of radiotherapy,T stage,TNM stage,D50 and Dmean were used to establish a neural net prediction model to predict the occurrence and grade of xerostomia.Results: 1.Follow-up ended September 2021,of a total of 462 patients included in the study,394 had xerostomia,accounting for 85.3% of all patients,and of 394 patients with xerostomia symptoms,203 had grade 2 or more.Three years after the end of radiotherapy,226 patients still had xerostomia,representing 48.7% of the total number(462),and,168 patients recovered from conscious xerostomia,accounting for 42.6% of all patients who had xerostomia(394).But of the 462 patients included in the study,only 12.1%,with a total of57,still had grade 2 and above after 3 years of radiotherapy.2.ROC curve analysis of parotid dose based on LTG showed that cutoff values for parotid dose D50,D50-L,D50-R,Dmean,Dmean-L and Dmean-R,respectively,and area AUC under the curve were greater than 0.5,indicating that the patient had increased risk of xerostomia after radiotherapy,and the results were statistically significant(P value less than 0.05).3.ROC curve analysis of parotid dose according to the HXG showed that cutoff values for parotid doses D50,D50-L,D50-R,Dmean,Dmean-L and Dmean-R were 28.66 Gy,23.12 Gy,29.04 Gy,28Gy,28.3Gy,35.55 Gy,respectively,and area AUC values under the curve were greater than 0.5 and patients with parotid dose higher than the cutoff,but P values above 0.05.4.Correlation analysis was performed based on the cutoff of parotid dose,and univariate analysis showed that beyond the cutoff of parotid dose increased LTG in forward xerostomia(P < 0.05),but had no effect on HXG at the most severe time(P > 0.05).D50-R>23.93 Gy and Dmean> 26 Gy were independent risk factors for the occurrence of xerostomia.But not associated with D50,D50-L,Dmean-L,and Dmean-R(P> 0.05).There was no correlation between the dose of parotid gland and the grade of xerostomia in the HXG(P > 0.05).5.The predictive model established through the MATLAB neural network,the HXG and LTG were predicted by entering the patient sex,radiotherapy,number of radiotherapy,T stage,TNM stage,D50-L,D50-R,Dmean-L and Dmean-R.The model showed good fit in the training,test and validation groups and the overall R values was 0.82256.Conclusion: The incidence of xerostomia in this study was 85.3%,and the incidence of forward xerostomia(more than 3 years after the end of radiotherapy)was 48.7%.In the three years after the end of radiotherapy,42.6% of patients fully recovered from xerostomia.D50-R> 23.93 Gy and Dmean> 26 Gy are independent risk factors for the development of xerostommia.It is feasible to use the parotid gland dose to predict the occurrence and grade of xerostomia in patients with nasopharyngeal carcinoma.Furthermore,the patient’s gender,radiation method,number of radiation therapy,stage T and TNM stage were also predictive.