Phase 3 comparison of high-dose once-daily (QD) thoracic radiotherapy (TRT) with standard twice-daily (BID) TRT in limited stage small cell lung cancer (LSCLC): CALGB 30610 (Alliance)/RTOG 0538.

8505 Background: Although level 1 evidence is lacking, the majority of patients (pts) with LSCLC are treated with a high dose QD TRT regimen in clinical practice. CALGB 30610/RTOG 0538 was designed to determine if administering high dose TRT would improve overall survival (OS), compared with standard 45 Gy BID TRT, in LSCLC pts treated with chemoradiotherapy. Methods: Eligible pts had LSCLC, ECOG performance status (PS) 0-2 and regional lymph node involvement excluding contralateral hilar or supraclavicular nodes. This phase 3 trial was conducted in 2 stages. In the first stage, pts were randomized 1:1:1 to 45 Gy BID over 3 weeks, 70 Gy QD over 7 weeks, or 61.2 Gy concomitant boost (CB) over 5 weeks. For the second stage, the study planned discontinuation of one high dose arm based on interim toxicity analysis with patients then randomized 1:1 in the two remaining arms. TRT was given starting with either the 1 st or 2 nd (of 4 total) chemotherapy cycles. The primary endpoint was OS measured from date of randomization. Results: The trial opened 03/15/2008 and closed 12/01/2019 upon completing accrual, with the CB arm discontinued 3/11/2013 after interim analysis. This analysis includes 638 pts randomized to 45 Gy BID TRT (n = 313) or 70 Gy QD TRT (n = 325). Median age was 63 years (range 37-81), the majority of pts were Caucasian (86%), female (52%), and with ECOG PS 0-1 (95%). After median follow-up of 2.84 years (IQR:1.35 -5.61) for surviving pts, QD compared to BID did not result in a significant difference in OS (HR 0.94, 95% CI: 0.76-1.2, p = 0.9). Median, 2- and 4-year OS for QD were 30.5 months (95% CI: 24.4-39.6), 56% (95% CI: 0.51-0.62), and 39% (95% CI: 0.33-0.45), and for BID 28.7 months (95% CI: 26.2-35.5), 59% (95% CI: 0.53-0.65), and 35% (95% CI: 0.29-0.42). QD also did not result in a significant difference in PFS (HR 0.96, 95% CI: 0.78-1.18, p = 0.94). Most grade 3+ hematologic and non-hematologic adverse events (AEs) were similar between cohorts. Rates of grade 3+ febrile neutropenia, dyspnea, esophageal pain and dysphagia for QD were 12.6%,7%, 11.6% and 11.3%, and for BID 13.6%, 4%, 11.2 % and 9.5%. Grade 5 AEs were reported in 3.7% and 1.7% of the QD and BID cohorts, respectively. Results will be updated at presentation. Conclusions: High dose QD TRT to 70 Gy did not significantly improve OS compared with standard 45 Gy BID TRT. Nevertheless, favorable outcomes on the QD arm provide the most robust evidence available supporting high dose once-daily TRT as an acceptable option in LSCLC. Outcomes from this study, the largest conducted in LSCLC to date, will help guide TRT decisions for this patient population. Support: U10CA180821, U10CA180882; Clinical trial information: NCT00632853.