KEY POINTS
- The multicentre retrospective study included 946 patients with limited-stage SCLC treated with curative platinum-based chemoradiotherapy from 2016–2025. Propensity matching produced 265 patients per group with or without a dedicated CTV.
- Conventional planning expanded the GTV by 5–8 mm to create the CTV, followed by a 5–10-mm PTV margin. In the omission group, the prescription-bearing PTV was generated directly from the GTV without an additional microscopic-disease expansion.
- Thoracic RT was predominantly IMRT using either 60–66 Gy once daily or 45 Gy twice daily, with most patients receiving concurrent platinum-based chemoradiotherapy.
- Efficacy was similar after matching. Median PFS was 11.8 versus 11.6 months for omit-CTV versus CTV (HR 0.93; p=0.50), while median OS was 35.8 versus 30.7 months (HR 0.85; p=0.22). Objective response rates were 72.8% versus 69.4%.
- There was no significant difference in local recurrence patterns (p=0.561), arguing against an obvious geographic-miss penalty from removing the conventional CTV expansion.
- Toxicity moved in the opposite direction. Grade ≥3 radiation pneumonitis fell from 8.3% to 3.4% (p=0.004), while grade ≥3 esophagitis decreased from 9.1% to 5.7% (p=0.037) with CTV omission.
- The immunotherapy subgroup contained only 77 patients but generated an intriguing exploratory signal: from immunotherapy initiation, median PFS was 22.8 versus 12.5 months (HR 0.45) and OS was not reached versus 25.6 months (HR 0.29). Omit-CTV patients also had higher nadir lymphocyte counts, but these observational findings cannot establish an immune-mediated survival benefit.
CLINICAL TAKEAWAY
Routine microscopic CTV expansion may not be necessary for every LS-SCLC patient treated with modern image-guided chemoradiotherapy, and reducing irradiated volume could materially reduce thoracic toxicity. The matched data are compelling enough for prospective testing, but not sufficient to replace current contouring standards on their own.