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.