The optimal dose of radiotherapy (RT) to palliate symptomatic advanced lung cancer is unclear. We systematically reviewed randomized controlled trials (RCTs) of palliative thoracic RT. RCTs comparing two or more dose fractionation schedules were reviewed using the random-effects model of a freely available information management system. The relative risk and 95% CI for each outcome were presented in Forrest plots. Exploratory analysis comparing dose schedules after conversion to the time-adjusted biologically equivalent dose (BED) was performed to investigate for a dose-response relationship. A total of 13 RCTs involving 3,473 randomly assigned patients were identified. Outcomes included symptom palliation, overall survival, toxicity, and reirradiation rate. For symptom control in assessable patients, lower-dose (LD) RT was comparable with higher-dose (HD), except for the total symptom score (TSS): 65.4% of LD and 77.1% of HD patients had improved TSS (P = .003). Greater likelihood of symptom improvement was seen with schedules of 35 Gy(10) versus lower BED. At 1 year after HD and LD RT, 26.5% versus 21.7% of patients were alive, respectively (P = .002). Sensitivity analysis suggests this survival improvement was seen with 35 Gy(10) BED schedules compared with LDs. Physician-assessed dysphagia was significantly greater in the HD arm (20.5% v 14.9%; P = .01), and the likelihood of reirradiation was 1.2-fold higher after LD RT. No significant differences were observed for specific symptom-control end points, although improvement in survival favored HD RT. Consideration of palliative thoracic RT of at least 35 Gy(10) BED may therefore be warranted, but must be weighed against increased toxicity and greater time investment.