Radiation-induced xerostomia and oncologic outcomes in nasopharyngeal carcinoma treated with comprehensive salivary gland-sparing helical tomotherapy: a prospective study of 266 patients

Objective: To evaluate whether comprehensive salivary gland-sparing helical tomotherapy (HT) can reduce radiation-induced xerostomia without compromising locoregional control or survival in patients with nasopharyngeal carcinoma (NPC). Methods: A total of 266 patients with NPC treated with HT were prospectively analyzed. A comprehensive salivary gland-sparing planning strategy, including preservation of the parotid glands and other salivary structures whenever clinically feasible, was applied to minimize irradiation of salivary glands. Xerostomia was assessed using patient-reported outcome measures during follow-up. Acute and late toxicities were graded according to the RTOG/EORTC criteria. Overall survival (OS), cancer-specific survival (CSS), locoregional recurrence-free survival (LRRFS), and distant metastasis-free survival (DMFS) were estimated using the Kaplan-Meier method. Results: With a median follow-up of 70.5 months, patients showed significant improvement in xerostomia symptoms. Late xerostomia was observed in 26 patients (9.8%) with Grade I-II, and only one patient (0.4%) developed Grade III xerostomia. The 1-, 3-, and 5-year overall survival (OS) rates were 95.9%, 86.8%, and 81.6%, respectively, while the corresponding cancer-specific survival (CSS) rates were 98.1%, 92.6%, and 90.2%. Locoregional control remained excellent, with a locoregional recurrence rate of 7.5% and a 5-year locoregional recurrence-free survival (LRRFS) of 92.1%. No grade 4 acute or late toxicity was observed. Multivariate Cox regression analysis demonstrated that age was significantly associated with survival outcomes (OS: p = 0.01; CSS: p = 0.01). Conclusions: Comprehensive salivary gland-sparing helical tomotherapy reduces radiation-induced xerostomia without compromising locoregional control or survival, supporting its oncologic safety in NPC radiotherapy. Clinical trial registration: https://www.chictr.org.cn/showproj.html?proj=17360, identifier ChiCTR-ONN-17010597.