Long-term outcome and late toxicities of simultaneous integrated boost-intensity modulated radiotherapy in pediatric and adolescent nasopharyngeal carcinoma

The application of simultaneous integrated boost-intensity modulated radiotherapy （SIB-IMRT） in pediatric and adolescent nasopharyngeal carcinoma （NPC） is underevaluated. This study aimed to evaluate long-term outcome and late toxicities in pediatric and adolescent NPC after SIB-IMRT combined with chemotherapy. Thirty-four patients （aged 8-20 years） with histologically proven, non-disseminated NPC treated with SIB-IMRT were enrolled in this retrospective study. The disease stage distribution was as follows： stage I, 1 （2.9%）; stage III, 14 （41.2%）; and stage IV, 19 （55.9%）. All patients underwent SIB- IMRT and 30 patients also underwent cisplatin-based chemotherapy. The prescribed dose of IMRT was 64-68 Gy in 29-31 fractions to the nasopharyngeal gross target volume. Within the median follow-up of 52 months （range, 9-111 months）, 1 patient （2.9%） experienced local recurrence and 4 （11.8%） developed distant metastasis （to the lung in 3 cases and to multiple organs in 1 case）. Four patients （11.8%） died due to recurrence or metastasis. The 5-year Iocoregional relapse-free survival, distant metastasis-free survival, disease-free survival, and overall survival rates were 97.1%, 88.2%, 85.3%, and 88.2%, respectively. The most common acute toxicities were grades 3-4 hematologic toxicities and stomatitis. Of the 24 patients who survived for more than 2 years, 16 （66.7%） and 15 （62.5%） developed grades 1-2 xerostomia and ototoxicity, respectively. Two patients （8.3%） developed grade 3 ototoxicity; no grade 4 toxicities were observed. SIB-IMRT combined with chemotherapy achieves excellent long-term Iocoregional control in pediatric and adolescent NPC, with mild incidence of late toxicities. Distant metastasis is the predominant mode of failure.