Background: Prophylactic cranial irradiation reduces the incidence of brain metastasis in patients with small-cell lung cancer. Whether this treatment, when given to patients in complete remission, improves survival is not known. We performed a meta-analysis to determine whether prophylactic cranial irradiation prolongs survival. Methods: We analyzed individual data on 987 patients with small-cell lung cancer in complete remission who took part in seven trials that compared prophylactic cranial irradiation with no prophylactic cranial irradiation. The main end point was survival. Results: The relative risk of death in the treatment group as compared with the control group was 0.84 (95 percent confidence interval, 0.73 to 0.97; P = 0.01), which corresponds to a 5.4 percent increase in the rate of survival at three years (15.3 percent in the control group vs. 20.7 percent in the treatment group). Prophylactic cranial irradiation also increased the rate of disease-free survival (relative risk of recurrence or death, 0.75; 95 percent confidence interval, 0.65 to 0.86; P<0.001) and decreased the cumulative incidence of brain metastasis (relative risk, 0.46; 95 percent confidence interval, 0.38 to 0.57; P<0.001). Larger doses of radiation led to greater decreases in the risk of brain metastasis, according to an analysis of four total doses (8 Gy, 24 to 25 Gy, 30 Gy, and 36 to 40 Gy) (P for trend=0.02), but the effect on survival did not differ significantly according to the dose. We also identified a trend (P=0.01) toward a decrease in the risk of brain metastasis with earlier administration of cranial irradiation after the initiation of induction chemotherapy. Conclusions: Prophylactic cranial irradiation improves both overall survival and disease-free survival among patients with small-cell lung cancer in complete remission.
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