Comparing outcomes and toxicities among patients with nasopharyngeal carcinoma treated with daytime versus evening radiotherapy: A retrospective analysis with propensity score matching

To compare survival outcomes and acute toxicities between daytime and evening radiotherapy (RT) in patients with nasopharyngeal carcinoma (NPC). We enrolled 1351 NPC patients who received definitive RT in the daytime (before 16:00; n = 625) or evening (after 16:00; n = 726) between 2015 and 2016. Optimal cutoff time was determined by receiver operating characteristic analysis. Survival outcomes and toxicities were compared between groups before and after propensity score matching (PSM). Multivariate Cox analyses were performed to identify independent prognostic factors. With a median follow-up of 63 months, evening RT showed better overall survival (OS; p = 0.020), progression-free survival (PFS; p = 0.035), and locoregional failure-free survival (LRFS; p = 0.037), compared with daytime RT, but not distant metastasis-free survival (p = 0.523). Evening RT showed a lower incidence of all-grade dermatitis (59.5% vs. 68.2%, p = 0.002). After PSM, RT time remained an independent prognostic factor for LRFS (HR = 0.601, p = 0.018), OS (HR = 0.643, p = 0.043), and PFS (HR = 0.754, p = 0.040). Subgroup analyses revealed that evening RT improved OS (p = 0.007) and PFS (p = 0.006) in females and LRFS (p = 0.035) in males, with more pronounced benefits in older females (≥45 years; OS: p = 0.027, PFS: p = 0.003) and reduced mucositis in older males (82.9% vs. 91.4%, p = 0.015). Overall, evening RT demonstrated superior survival outcomes and reduced acute toxicities in NPC patients, with distinct benefits across sex and age.