Investigation of the feasibility of elective irradiation to neck level Ib using intensity-modulated radiotherapy for patients with nasopharyngeal carcinoma: a retrospective analysis.

Multivariable analysis to adjust for various risk factors demonstrated a DLN-IIa ≥ 20 mm or level IIa LNs with ES (HR 2.21; 95 % confidence interval [CI] 1.10–4.46; P = .026) and oropharynx involvement (HR 2.59; 95 % CI 1.18–5.69; P = .018) were independently significantly associated with metastasis to the level Ib LNs at diagnosis, while positive bilateral CLNs (HR 1.95; 95 % CI 0.97–3.92; P = .061) had a borderline significant association with metastasis to the level Ib LNs at diagnosis (Table 2 ).

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