MA 01.11 Timing of Thoracic Radiotherapy is More Important Than Dose Escalation in Patients with Limited-Stage Small Cell Lung Cancer

The optimal thoracic radiation dose/fraction for limited-stage small cell lung cancer (SCLC) is still in debate. This study mainly aims to retrospectively compare the impact on local/regional progression-free survival (LRPFS) of different thoracic radiation dose/fraction schedules from two prospective trials. Patients in the hyperfractionated arm received thoracic radiotherapy consisted of 1.5 Gy twice a day in 30 fractions to 45 Gy. Patients in the hypofractionated arm received 2.5 Gy daily in 22 fractions to 55 Gy. Kaplan-Meier method was used to estimate survival data. Multivariate prognosis analysis was made by Cox proportional hazard regression analysis. Nighty-two and 96 patients were accrued into to the hyperfractionated and hypofractionated arm respectively. The 1-year, 2-year LRPFS rates of the two arms were 82.1%, 60.7% and 84.9%, 68.8% respectively (P=0.27). The median OS time (months) of the two arms were 28.3 and 22.0 respectively, while 1-year, 3-year, 5-year OS rates were 85.2%, 40.8%, 27.1% and 76.9%, 34.3%, 26.8% respectively (P=0.37). On multivariate Cox regression study, the time (days) from the initiation of chemotherapy to thoracic radiotherapy (TCT) ≤ 43 (HR: 0.397, 95%CI: 0.207-0.762, P=0.005) was independently associate with improved LRPFS. The time (days) from the start of chemotherapy to end of thoracic radiotherapy (SER) ≤63 (HR: 0.508, 95%CI: 0.322-0.762, P=0.044) and PCI (HR: 0.433, 95%CI: 0.298-0.630, P=0.000) were favorably related to OS. Grade 2 and 3 acute radiation esophagitis were observed in 28.3%, 8.7% and 15.5%, 2.1% of patients in hyper- and hypofractionated arm respectively (P=0.009). Both hyperfractionated and hypofractionated radiotherapy had achieved good LRPFS and OS in this study, although there was no statistical significance between the two arms. Keep TCT ≤ 43, SER ≤ 63 resulted in better LRPFS and OS. However, the incidence of acute radiation induced esophagitis was significantly more common in the hyperfractionated arm than in hypofractionated arm.