Assessment of Salivary Function Change in Nasopharyngeal Carcinoma Treated by Parotid-Sparing Radiotherapy

Abstract

The purpose of this study was to evaluate function of major salivary glands, subjective xerostomia, and correlation between subjective and objective xerostomia scoring after precision-oriented radiotherapy for nasopharyngeal carcinoma. From 2000 to 2002, 34 patients with histologically proven non-metastatic nasopharyngeal carcinoma received definitive therapy by parotid-sparing radiotherapy, which included intensity-modulated radiotherapy (33 patients>60 Gy), 3D-conformal radiotherapy, and brachytherapy boost. Salivary function was assessed by sialoscintigraphy pre-irradiation and post-irradiation at 1, 6, 12, and 18 months. The salivary stimulated secretion ratio (SSR) was used to evaluate function of submandibular and parotid glands. Subjective and objective xerostomia was monitored by the LENT/SOMA system. The median dose to parotid gland was 34.6 Gy (interquartile range, 32.9-36.5 Gy). The median dose to submandibular gland was 60.5 Gy (interquartile range, 58.1-61.5 Gy). Parotid-gland post-irradiation median SSR at 1 (0.01, P=0.000) and 6 (0.08, P=0.002) months showed significant reduction compared with pre-irradiation data (0.30). After 12 months, parotid-gland median SSR (12 months, 0.22, P = 0.734; 18 months, 0.16, P=0.885) lost significance compared with pre-irradiation data. Submandibular-gland post-irradiation median SSR at 1 (P=0.000), 6 (P=0.000), 12 (P=0.000), and 18 (P=0.000) months all showed significant reduction compared with pre-irradiation data. There were significant correlations between LENT/SOMA subjective and objective xerostomia scores at 6 months (r=0.657, P=0.000), 12 months (r=0.480, P=0.013), and 18 months (r=0.591, P=0.002). With parotid-sparing radiotherapy for nasopharyngeal carcinoma, gland function can recover significantly 12 months after radiotherapy. There were significant rank-order correlations between LENT/SOMA subjective and objective (analytic) grading scores at 6 to 18 months' follow-up.