Effects of thoracic radiotherapy timing and duration on progression-free survival in limited-stage small cell lung cancer.

Concurrent chemoradiotherapy (CRT) has been recommended and applied widely as the standard treatment for limited-stage small cell lung cancer (LS-SCLC). However, controversies remain regarding the optimal timing and treatment duration of thoracic radiotherapy (TRT), and their effects on patient survival. To evaluate prognostic values of TRT timing and duration on progression-free survival (PFS) in LS-SCLC and their dependence on TRT fractionation and clinicopathological characteristics, we retrospectively analyzed 197 LS-SCLC patients receiving CRT from 2000 to 2016 at Sun Yat-sen University Cancer Center. Based on the optimal cut-off values of TRT timing and duration generated by Cutoff Finder, patients were divided into early TRT/late TRT group and short TRT/long TRT group respectively. Univariate and multivariate Cox analysis were performed to assess correlations of TRT timing, duration, fractionation, and clinicopathological characteristics with PFS. Univariate analysis revealed that early-initiated TRT (P = 2.54 × 10-4 ) and short TRT (P = .001) significantly correlated with longer PFS. Their PFS benefits persisted in patients receiving hyperfractionated TRT and etoposide-cisplatin (EP) chemotherapy, but were less prominent in those receiving once-daily TRT and non-EP chemotherapy. Multivariate analysis further identified early initiated TRT (P = .004) and short TRT (P = .017) as independent prognostic factors for longer PFS in LS-SCLC. Our study confirmed that early-initiated TRT and short TRT had positive prognostic roles in LS-SCLC, especially in patients receiving hyperfractionated TRT and etoposide-cisplatin chemotherapy. TRT fractionation was not an independent prognostic factor in LS-SCLC.