Significance of boost dose for T4 nasopharyngeal carcinoma with residual primary lesion after intensity-modulated radiotherapy

Background Previous studies showed poorer survival in T4 disease with residual lesion. To evaluate the efficacy and toxicity of a boost dose for T4 nasopharyngeal carcinoma (NPC), patients with a residual primary lesion after intensity-modulated radiotherapy (IMRT). Methods 398 T4 NPC patients with residual primary lesions after radical IMRT were retrospectively reviewed. An IMRT boost dose of 4-6.75 Gy was delivered to the residual lesions in 2-3 fractions. Propensity score matching (PSM) was applied to balance potential confounders between groups (ratio, 1:2). The presence of Epstein-Barr virus (EBV) DNA in plasma after IMRT was used for risk stratification. Results Patients who received boost radiation had significantly improved overall survival (OS) and local recurrence-free survival (LRFS) compared with those who did not (all P < 0.05). In the matched cohort, 3-year OS was 86.6% in the boost radiation group and 72.7% in the non-boost group (P = 0.022). Three-year LRFS was 93.4% in the boost radiation group and 83.5% in the non-boost group (P = 0.022). In the subgroup analysis, boost dose was shown to significantly improve 3-year OS (88.0% vs. 74.1%, P = 0.021) in the low-risk group (with undetectable plasma EBV DNA after IMRT). The administration of a boost dose also improved 3-year OS in the high-risk group (with detectable plasma EBV DNA after IMRT) (66.7% vs. 60.0%, P = 0.375). Multivariate analysis demonstrated that boost dose was the only protective prognostic factor. Conclusion The addition of a boost dose for T4 NPC patients with residual primary lesion after radical IMRT provides satisfactory tumor control and clinical benefit. Additional timely and effective strengthening treatments are recommended for patients with detectable levels of plasma EBV DNA after radiotherapy.