ABSTRACT
Objective:To investigate the effects of estimated dose of radiation to immune cells (EDRIC) on overall survival (OS), local progression-free survival (LPFS) and distant metastasis-free survival (DMFS) in limited-stage small-cell lung cancer (LS-SCLC) with different tumor burdens.Methods:Clinical data of 216 patients with LS-SCLC who initially received conventional fractionated radiotherapy of the chest for radical treatment in Tianjin Medical University Cancer Institute and Hospital from 2013 to 2019 were retrospectively analyzed. EDRIC was calculated based on the model developed by Jin et al. and tumor burdens were assessed by gross tumor volume (GTV) or clinical stage. The study endpoints were OS, LPFS and DMFS, which were calculated from the date of diagnosis. The optimal cut-off value of EDRIC was calculated by R language. The correlation between EDRIC and tumor burdens was analyzed using Spearman's correlations. Survival analysis was performed by Cox proportional hazards regression model and Kaplan-Meier curve. Results:The median follow-up time for the whole group was 47.8 months, and the median OS and DMFS was 34.6 months and 18.5 months, respectively, while the median LPFS did not reach. The optimal cut-off value of EDRIC was 6.8 Gy. Cox multivariate analysis showed that EDRIC was an independent prognostic factor affecting OS and DMFS. EDRIC was weakly correlated with GTV or clinical stage. Stratified by the median GTV, OS ( P=0.021) and DMFS ( P=0.030) were significantly shortened and LPFS had a tendency of shortening ( P=0.107) when EDRIC>6.8 Gy compared with those when EDRIC ≤ 6.8 Gy in the GTV ≤ 34.6 cm 3 group; EDRIC had little effect on OS, LPFS, and DMFS ( P=0.133, 0.420, 0.374) in the GTV>34.6 cm 3 group. Stratified by clinical stage, OS ( P=0.003) and DMFS ( P=0.032) were significantly shortened and LPFS ( P=0.125) tended to shorten when EDRIC>6.8 Gy in stage I, II and IIIA groups; EDRIC exerted slight effect on OS, LPFS, and DMFS ( P=0.377, 0.439, 0.484) in stage IIIB and IIIC groups. Conclusion:EDRIC is an important factor affecting prognosis and exerts more significant impact on prognosis in patients with smaller tumor burden.