Neck level Ib-sparing versus level Ib-irradiation in intensity-modulated radiotherapy for the treatment of nasopharyngeal carcinoma with high-risk factors: A propensity score-matched cohort study

Aim Level Ib lymph nodes metastasis is rare in nasopharyngeal carcinoma (NPC). We aimed to evaluate the feasibility of sparing level Ib-irradiation in NPC patients with high-risk factors. Materials and methods Four hundred forty-three NPC patients with radiologic extranodal extension (rENE) or level II lymph node maximal axial diameter (MAD) ≥ 20 mm treated by intensity-modulated radiotherapy (IMRT) between 2009 and 2012 were included in this study. Propensity score matching (PSM) was applied to balance potential prognostic factors (including age, sex, T and N stage, pretreatment EBV DNA level, and level II rENE and MAD) between patients who received and omitted level Ib irradiation. Kaplan–Meier analysis and the log-rank test were used to compare regional survival outcomes. Results PSM resulted in 169 matched pairs of eligible patients. The median follow-up period was 119 months in the matched cohort. The number of level Ib failure in the level Ib-sparing and level-Ib irradiation groups were 3/169 (1.8 %) vs 2/169 (1.2 %), P > 0.999. And the 5-year regional relapse-free survival (RRFS) rates of the two groups were 88.4 % vs 92.6 %, respectively. After PSM, RRFS (hazard ratio [HR]: 1.508, 95 % confidence interval [CI]: 0.762–2.986, P = 0.239), OS (HR: 1.219, 95 % CI: 0.754–1.972, P = 0.418), distant metastasis-free survival (DMFS) (HR: 1.605, 95 % CI: 0.900–2.863, P = 0.109), and local relapse-free (LRFS) (HR: 0.956, 95 % CI: 0.436–2.095, P = 0.910) were similar in the two arms. The incidence of grade ≥ 1 dry mouth after 5 years was higher in the level Ib-irradiation group (27.5 % vs 16.5 %, P = 0.029). However, the incidences of grade 3–4 late toxicities were similar between the two groups. Conclusion Neck level Ib-sparing appears to be safe and feasible in NPC patients with rENE or level II MAD ≥ 20 mm and negative level Ib lymph nodes. Compared with cervical level Ib-irradiation, omission of irradiation to level Ib provides less dry mouth symptom.