154 - Is Clinical Target Volume Necessary in Limited-Stage Small Cell Lung Cancer? A Large-Scale Comparative Study

08:00am - 08:10am ET

Room 157

Presenter(s)

Xiaolong Wang, MS - Shandong Cancer Hospital and Institute, jinan, Shandong

X. Wang¹, Y. Chen¹, X. Yu², K. Zhao¹, Y. Li¹, J. Yu³, and X. Meng⁴; ¹Cancer Center, Shandong University, Department of Radiation Oncology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, Shandong, China, ²Cancer Center, Shandong University, Department of Radiation Oncology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, Shandong, China, ³Shandong Provincial Key Laboratory of Precision Oncology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, Shandong, China, ⁴Department of Radiation Oncology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, China

Purpose/Objective(s):

In limited-stage small cell lung cancer (LS-SCLC), the continued practice of adding a clinical target volume (CTV) margin creates a dilemma: it theoretically covers microscopic disease but inevitably exacerbates normal tissue injury. Whether this “safety margin” is truly required—especially with modern systemic therapies—is unknown. Our objective was to determine whether omitting the CTV could preserve efficacy while reducing toxicity compared with conventional delineation, and to assess the strategy’s potential survival advantage in immunotherapy-treated patients.

Materials/Methods:

A total of 926 patients with LS-SCLC were accrued for this study between February 2016 and February 2025. According to radiotherapy strategy, patients were classified into an Omit-CTV (n = 402) group and a CTV group (n = 524). To minimize selection bias, propensity score matching (1:1 ratio, caliper 0.02) was performed, yielding a balanced final analytical cohort of 532 patients (266 per arm). Primary endpoints were progression-free survival (PFS) and overall survival (OS). Secondary endpoints included first-failure patterns and treatment-related toxicity.

Results:

At a median follow-up of 29.9 months, response assessments revealed no compromise in efficacy (ORR: 72.9% with CTV vs. 70.3% with Omit-CTV). Long-term survival outcomes remained comparable: median PFS was 13.0 months in the CTV group versus 12.8 months in the Omit-CTV group (HR, 0.99; 95% CI, 0.80–1.22; P = .896), while median OS was 33.2 months and 37.2 months, respectively (HR, 1.23; 95% CI, 0.94–1.62; P = .132). No statistically significant difference was observed in local recurrence rates (23.3% vs. 30.8%; P = .217). Notably, compared with CTV, Omit-CTV was associated with lower rates of radiation pneumonitis (Grade 1–2: 19.9% vs. 28.9%; Grade =3: 0.8% vs. 6.4%; P < .001) and radiation esophagitis (Grade 1–2: 34.2% vs. 51.9%; P < .001). Among patients receiving immunotherapy, omitting CTV yielded a prolonged median PFS of 20.8 months versus 13.9 months with CTV (HR, 2.03; 95% CI, 1.00–4.14; P = .047). This advantage also extended to OS, where the median remained unreached in the Omit-CTV cohort as opposed to 22.2 months in the CTV cohort (HR, 4.01; 95% CI, 1.52–10.61; P = .003).

Conclusion:

In these large-scale cohorts, Omit-CTV demonstrated non-inferior efficacy and significantly lower toxicity compared with conventional delineation, alongside a potential survival benefit for patients receiving immunotherapy, collectively warranting further prospective validation of this strategy.