2191 - Timing of Once-Daily Thoracic Radiotherapy and Clinical Outcomes in Patients with Limited-Stage Small Cell Lung Cancer Treated with Concurrent Chemoradiotherapy

T. Zhan¹, X. Liu¹, W. Wang¹, L. Deng¹, T. Zhang¹, X. Wang¹, J. Wang², W. Liu Jr¹, F. Qinfu¹, Y. Zhai³, Z. Xiao³, N. Bi¹, Z. Zhou³, and Y. X. Li³; ¹Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences (CAMS) and Peking Union Medical College (PUMC), Beijing, China, ²Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing, China, ³Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China

Purpose/Objective(s): We aimed to investigate the timing of once-daily thoracic radiotherapy (TTRT) in patients with limited-stage small cell lung cancer (LS-SCLC) in the first-line concurrent chemoradiotherapy era. Materials/

Methods: A total of 445 patients with LS-SCLC receiving concurrent chemoradiotherapy were reviewed. Nonlinear analysis by restricted cubic splines was used to determine the relationship between timing of TRT (TTRT) and PFS or OS. OS and PFS in different TTRT groups were compared using log-rank tests and multivariable analyses. The cumulative incidence of locoregional recurrence (LRR), brain metastases (BM), and extracranial distant metastases (EDM) were investigated using competing risk analyses. Adverse events were also compared.
Results: The median duration of follow-up was 64 months. There was a non-linear relationship between TTRT and PFS (P = 0.002) or OS (P < 0.001). When TRT started from 31 days to 63 days, improved 5-year PFS (37.0%; P = 0.001) and OS (49.7%; P < 0.001) and decreased 5-year EDM (27.9%; P = 0.009) were achieved compared with the =30-day group (19.5%; 32.0%; 43.3%) and >63-day group (23.7%; 24.2%; 43.5%). However, no significant difference in overall survival was observed in groups divided by actual chemotherapy cycle. A downward trend was seen in the incidence of myelosuppression of grade 3–4 in different TTRT groups (P = 0.04).
Conclusion: Appropriate treatment timing window might exist in once-daily TRT with concurrent chemotherapy. Delaying in combination of TRT and prescribed chemotherapy cycle may impair the survival outcomes.