Prognostic Value of Metabolic Tumor Volume for Locally Advanced Non-Small Cell Lung Cancer Patients Treated with Definitive Radiotherapy without Chemotherapy: A Modern Experience

Abstract Purpose: Optimal treatment techniques and expected outcomes are largely undefined for patients with locally advanced non-small cell lung cancer (LA-NSCLC) who are ineligible for combined modality therapy. We describe outcomes for a modern series of patients treated with radiotherapy alone and explore prognostic factors in this setting. Methods: We reviewed patients treated with thoracic radiotherapy alone for stage IIB-IIIC NSCLC (May 2014 - February 2021). Median progression-free survival (PFS) and overall survival (OS) were estimated using the Kaplan-Meier method. Clinical characteristics, including molecular markers and metabolic tumor volume (MTV), were tested as predictors of PFS and OS using Cox proportional hazards modeling. Results: Forty-five patients met eligibility criteria. Median follow-up duration for living patients was 21.8 months. Twenty-seven patients developed disease progression, and 27 died. Median PFS duration was 6.0 months; median OS was 14.9 months. Eight patients received salvage immunotherapy after progression. MTV was the only statistically significant predictor of PFS (HR [after log10 transformation] = 2.03, 95% CI 1.04-4.00, p=0.039) and OS (HR = 2.42, 95% CI 1.10-5.31, p=0.028). Median PFS for patients with low MTV was 8.9 months, and 5.0 months for those with high MTV. Median OS for patients with low MTV was 27.2 months, and 8.9 months for those with high MTV. Conclusion: Volumetric disease burden may be an important prognostic factor for LA-NSCLC patients treated with definitive radiotherapy without chemotherapy. As many of these patients are eligible for immunotherapy, trials combining radiotherapy and immunotherapy should be explored for this population.