Is there a place for optimizing thoracic radiotherapy in limited-stage small cell lung cancer after twenty years?

Thoracic radiotherapy(TRT)is one of the main treatments in limited-stage small cell lung cancer(LS-SCLC).Hyperfractionated TRT(45 Gy,1.5 Gy twice daily)has been the standard of care(SOC)since Turrisi and colleagues published the results of their clinical trial in 1999.Two meta-analyses have demonstrated the benefits of concurrent chemotherapy and TRT in terms of intrathoracic disease control at 2 years and 3-year overall survival(OS).The phase 2 trial by Grønberg et al(2016)comparing once-daily hypofractionated TRT to twice-daily hyperfractionated TRT in LS-SCLC found similar outcomes in both groups in terms of response rate,progression-free survival(PFS),grade 3-4 adverse effects,and OS.The CONVERT trial,published in 2017,failed to demonstrate the superiority of the conventional scheme(once-daily TRT)vs twice-daily radiotherapy,despite the application of modern radiotherapy techniques and a quality assurance programme,thus confirming the twice-daily hyperfractionated regimen as the SOC.At the 2020 American Society of Clinical Oncology(ASCO)annual meeting,Grønberg et al reported preliminary findings from a phase 2 trial comparing two different TRT dose regimens(45 Gy vs 60 Gy),both administered twice daily.Those data demonstrated a marked improvement in 2-year survival rates in the high dose arm(70.2%vs 46.1%,P=0.002),despite similar objective response rates and PFS outcomes.Those findings provide a new treatment alternative to consider:Hyperfractionated,high-dose TRT.However,the results of that trial will need to be validated in a large,randomized phase 3 study.The results of the phase 2 CALCG 30610 trial will help to clarify the optimal dose and regimen.The potential role of upfront immunotherapy,which early data suggest may improve OS,also needs to be determined.