1022 - Optimizing Nodal Target Delineation in Limited-Stage Small Cell Lung Cancer: A Large-Scale, Multi-Institutional Study

05:35pm - 05:40pm ET

Room 258

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 transition to involved-field irradiation (IFI) creates a clinical dilemma: whether to target involved-node irradiation (INI) or involved-node station irradiation (INSI). We aimed to determine whether INI maintains efficacy while reducing treatment-related toxicity, and to assess its potential survival benefit in the contemporary immunotherapy era.

Materials/Methods:

A total of 1,046 patients with LS-SCLC were accrued from multiple institutions between January 2018 and June 2025. Patients were categorized into an INSI group (n = 505) and an INI group (n = 279) based on radiotherapy strategy. We applied 1:1 propensity score matching with a caliper of 0.02 to minimize selection bias, generating a balanced cohort of 524 patients (262 per group). Primary endpoints were progression-free survival (PFS) and overall survival (OS); secondary endpoints included first-failure patterns and treatment-related toxicity.

Results:

With a median follow-up of 27.0 months, median PFS was 12.8 months in the INI group and 13.0 months in the INSI group (HR, 1.05; 95% CI, 0.85–1.30; P = .624). Median OS was 37.6 months versus 33.6 months, respectively (HR, 1.13; 95% CI, 0.85–1.50; P = .387). Overall failure rates (58.0% vs. 59.2%; P = .790) and locoregional recurrence rates (29.8% vs. 26.0%; P = .330) were not significantly different between groups. Crucially, compared with INSI, INI was associated with significantly lower rates of radiation pneumonitis (any grade: 17.2% vs. 30.2%; grade =3: 1.9% vs. 5.0%; P = .002) and radiation esophagitis (any grade: 31.7% vs. 44.7%; grade =3: 6.5% vs. 9.5%; P = .009). Pulmonary dosimetric parameters, including mean V5, V20, V30, and MLD, were also significantly reduced in the INI group (all P = .05). In the immunotherapy-treated subgroup, INI demonstrated a significantly prolonged median PFS of 20.7 months in the INI cohort versus 15.7 months in the INSI cohort (HR, 0.57; 95% CI, 0.33–0.98; P = .041). This gain was further reflected in OS, where the median was not reached in the INI group as opposed to 36.2 months in the INSI group (HR, 0.40; 95% CI, 0.17–0.95; P =.038). Furthermore, Spearman correlation analysis revealed that nadir absolute lymphocyte counts were inversely correlated with both log10 (GTV) (? = -0.319, P < .001) and log10 (PTV) (? = -0.384; P < .001).

Conclusion:

In this large-scale study, INI maintained comparable efficacy to INSI while significantly reducing treatment-related toxicity. Furthermore, a survival benefit was observed in the immunotherapy-treated subgroup, potentially mediated by lymphocyte preservation. These findings justify further prospective validation of INI as the preferred nodal targeting strategy for LS-SCLC.