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Thoracic twice-daily radiotherapy and brain metastasis in patients with small cell lung cancer.

8560 Background: Although thoracic twice-daily radiotherapy (TDRT) is one of standards of care for small cell lung cancer, its impact on brain metastases remains unknown. This study aimed to compare TDRT with once-daily radiotherapy (ODRT) for the brain metastases rate after prophylactic cranial irradiation in patients with small cell lung cancer. Methods: Consecutive patients received TDRT (45Gy/30f)/ODRT(50-66Gy/25-33f), chemotherapy and prophylactic cranial irradiation were retrieved from eight hospitals’ databases between 2003 and 2016. The endpoints included brain metastases, progression-free survival and overall survival. Brain metastases rate was evaluated using competing risk analysis. A 1:1 propensity score matching approach was used to control confounding between these two groups. Confounding covariates included eight demographic variables and eight treatment related covariates. Results: Of the 778 eligible patients with median age of 55-year (IQR, 48-61), 204 (26.2%) were female. At a median follow-up time of 23.6 months (IQR, 14.2- 38.2), 131 (16.8%) experienced brain metastases. The rates in TDRT were significantly higher than ODRT (3-year, 26.0% vs. 16.9%; HR = 1.55, 95%CI 1.06-2.26, P = 0.03). Of the 338 matched patients (169 in ODRT vs. 169 in TDRT), 60 (17.8%) experienced brain metastases with 3-year rate of 14.9% in ODRT vs 26.0% in TDRT (HR = 1.71, 95%CI 1.02-2.88, P = 0.04). Progression-free survival was similar in both the whole cohort and the matched one. Overall survival in ODRT tended to be significantly longer after matching (median, 47.2 months in ODRT vs. 32.8 months in TDRT; HR = 1.41, 95%CI 0.99-2.01, P = 0.06). When jointly evaluated biologically effective dose (BED), start of any therapy to the end of radiotherapy (SER) and TDRT/ODRT in the multivariable analysis, the impact of ODRT/TDRT on overall survival become more significant (HR = 1.69, 95%CI 1.05-2.71, P = 0.03). Conclusions: Patients with small cell lung cancer who were treated with thoracic TDRT appeared to have higher risk of brain metastases than those with ODRT, which strongly supports the need for further prospective randomized clinical trials, especially in China or other parts of Asia.