Relationship between radiation-induced xerostomia and the volume of parotid glands exposed in radiotherapy for nasopharyngeal carcinoma

Objective: To evaluate the relationship between the volume of parotid glands and radiation-induced xerostomia in patients with nasopharyngeal carcinoma (NPC). Methods: A total of 199 patients with NPC who were admitted to our hospital from 2015 to 2016 were enrolled as subjects. According to the initial volume of parotid glands, all patients were divided into large parotid group and small parotid group. The incidence of xerostomia after radiotherapy and dosimetric parameters were compared between the two groups. Comparison of categorical data was made by x² test. Comparison of continuous data was made by t-test or nonparametric test. Comparison of dose-volume histogram index was made by nonparametric test. Results: There was no difference in the severity of xerostomia between the two groups at 3 and 6 months after radiotherapy. At one year after radiotherapy, the large parotid group had significantly milder xerostomia than the small parotid group (P = 0.035). The small parotid group had a higher dose delivered to both parotid glands than the large parotid group. There was no difference in the mean dose to the submandibular gland between the two groups. Conclusions: The initial volume of parotid glands is one of the influencing factors for the grade of xerostomia after radiotherapy. Patients with large parotid glands have better recovery from xerostomia after radiotherapy than those with small parotid glands. For patients with small parotid glands, more attention should be paid to reducing the dose to protect parotid glands. (authors)