Background: Small cell lung cancer (SCLC) makes up 13% of lung malignancies. Only one-third of SCLC patients received their diagnosis at the limited stage. Treatment for symptomatic extensive-stage (ES) SCLC with persistent intrathoracic disease is still controversial. The present research aimed to analyze the impact of palliative thoracic radiotherapy (TRT) as a treatment for this patient group and build a prognostic nomogram. Methods: In this retrospective, multi-center study, we analyzed 120 patients with ES-SCLC and a World Health Organization performance status of 1-2 who were diagnosed between March 2014 and September 2019. A nomogram was formulated to predict the patients' 1- and 2-year overall survival (OS). Results: The study cohort had a median age of 62 years, and males accounted for 85% of enrollees. A significant extension was observed in the median OS in the TRT group compared to the no TRT group (P<0.001). When the patients were stratified by TRT dose, no significant differences in OS were noted (P=0.530). However, higher levels of inflammatory markers prior to TRT were associated with a shorter OS (neutrophil-to-lymphocyte ratio, P=0.002; platelet/lymphocyte ratio, P=0.023). The nomogram's Harrell's concordance (C)-statistic reached 0.70, and the calibration curve analysis revealed goodness of fit. Conclusions: The neutrophil-to-lymphocyte ratio is an independent factor predicting survival in ES-SCLC patients treated with palliative TRT. Our nomogram, which incorporates immunological markers, has higher accuracy than existing models for the prediction of individuals' chances of survival, and it could be a significant tool for clinicians in the development of tailored therapeutic strategies.