Twice-daily thoracic radiotherapy by intensity-modulated radiation therapy (IMRT) compared with simultaneous integrated boost IMRT (SIB-IMRT) with concurrent chemotherapy for patients with limited-stage small cell lung cancer. A propensity-score matched analysis

•The GTV of 57 Gy, CTV of 51 Gy, and PTV of 45 Gy are physically feasible.•Compared with IMRT, chemoradiotherapy by the SIB-IMRT approach may improve PFS.•The PSM method was used to balance the observable potential confounding factors. Concurrent chemoradiotherapy is the standard treatment for limited-stage small-cell lung cancer patients (SCLC). However, the optimal dose and schedule of thoracic radiotherapy (TRT) has not been established. We retrospectively reviewed the clinical records of limited-stage SCLC patients treated with twice-daily TRT and concurrent chemotherapy between December 2009 and December 2017. Patients were divided into two groups according to radiotherapy dose: the intensity modulated radiotherapy (IMRT) group [45 Gy to the planning target volume (PTV)] and the simultaneous integrated boost IMRT (SIB-IMRT) group (57 Gy to the gross tumour volume, 51 Gy to the clinical target volume, and 45 Gy to PTV). A 1:1 propensity score matching (PSM) was applied to balance the observable potential confounding factors between the two groups. Primary endpoint was progression-free survival (PFS). A total of 112 patients were enrolled in our study, including 71 patients in the IMRT group and 41 patients in the SIB-IMRT group. After PSM, the clinical features were well balanced between the groups, including 37 patients each. The median PFS was 17.54 months in the IMRT group versus 34.92 months in the SIB-IMRT group (P = 0.047). The median overall survival (OS) was 38.52 months in the IMRT group versus 63.41 months in the SIB-IMRT group (P = 0.261). Compared with IMRT, a high dose of twice-daily TRT by the SIB-IMRT approach with concurrent chemotherapy for limited-stage SCLC patients may improve PFS without increasing toxicities. However, PFS improvement failed to result in significant advantages in OS.