Small steps.

Top Line: What is the right dose for limited stage small cell lung cancer?

The Study: We already know from the CONVERT trial that 66 Gy in 33 QD fraction was similar but not superior to the standard BID regimen. The other large randomized trial to make this comparison is CALGB 30610/RTOG 0538. In the CALGB trial, 638 patients with limited stage SCLC were treated with 4 cycles of platinum and etoposide and concurrent radiation. They were randomized to receive 45 Gy in 30 BID fractions or 70 Gy in 35 QD fractions. There was no difference in median OS between QD and BID radiation (30.1 v 28.5 months). The rates of OS at 2 years (57% v 58%) and 5 years (33% v 29%) were also similar. Rates of disease response, recurrence, and toxicity were also comparable. One of the few differences was that a higher proportion of patients in the BID arm completed all planned radiation (92% v 79%). The trial was designed to show the superiority of QD treatment, which it didn’t. So while it is technically negative, the CALGB trial and CONVERT trial reassuringly show no obvious detriment to QD treatment. So what is going on in the real world? A survey of US radiation oncologists found that most used QD fractionation for SCLC and the most common dose was 60 Gy in 30 fractions. In fact, an informal poll on theMedNet shows that most respondents used 60 Gy in 30 fractions. This is likely influenced by the adoption of 60 Gy in 30 fractions for NSCLC after RTOG 0617 and the logistical challenges of BID treatment. Now we have the CONVERT and CALGB trials that show at least 66-70 Gy is necessary to expect comparable outcomes to 45 Gy BID. On the other hand, there is serious uncertainty about the effect of dose escalation beyond 60 Gy on cardiac events from the NSCLC literature. While SCLC and NSCLC are two different diseases, the OARs effected by radiation dose are the same. Many think the way forward for SCLC radiation will likely be through BID dose escalation or hypofractionation.

TBL: 70 Gy in 35 fractions is still not superior to 45 Gy in 30 BID fractions when treating limited stage SCLC. | Bogard J Clin Oncol 2023