Association of irradiation dose and increased incidence of xerostomia inpatients with nasopharyngeal carcinoma

Objective: To identify risk factors for post-radiation xerostomia and to evaluate the tolerance to doses administered to the parotid gland in patients with nasopharyngeal carcinoma (NPC). Methods: A total of 462 patients with NPC who received radiotherapy at Nanfang Hospital of Southern Medical University and Sichuan Cancer Hospital from 2012 to 2016 were retrospectively analyzed. Xerostomia was diagnosed according to the Radiation Therapy and Oncology Group (RTOG) grade. Medcalc software and SPSS software were used for statistical analysis, and MATLAB and R software was used for modeling. Results: The cut-off values for Dmean (the average dose of parotid), Dmean-L (the average dose of left parotid) and D50-R (dose received at 50% volume of right parotid) were 26.00, 28.30 and 23.93 Gy, above which the risk of long-time xerostomia occurs is increased (P < 0.05). D50, D50-L, D50-R, Dmean, Dmean-L and Dmean-R were 28.66, 23.12, 29.04, 28.00, 28.30 and 35.55 Gy, respectively, but the results showed that this dose was not associated with highest xerostomia grade (HXG) (P > 0.05). The relevant factors were independent risk factors for the development of xerostomia, the same was true for age, T stage, and D-PTV (dose of PTV). Using patient's gender, radiation treatment, number of radiotherapy sessions, T stage, TNM stage, Dmean and D50 (dose received at 50% volume of the parotid glands) to established a prediction model to predict HXG and long-term xerostomia grading (LTG), the results indicated that Training showed R = 0.82. The independent risk factors were included to establish the nomogram prediction model. The results showed that the C-index was 0.671. Conclusion: It is feasible to establish a neural network model or a nomogram prediction model using parotid dose parameters to predict the incidence of radiation-induced xerostomia.