2511 - Reirradiation or Repeat Organ Irradiation for Non-Small Cell Lung Cancer: Oncological Outcomes and Toxicities
Presenter(s)
J. Willmann1,2, K. Dähler1, M. Day1, K. Kefer1, N. Torelli1, J. von der Grün1, A. Joye1, M. C. Mayinger1, S. Tanadini-Lang1, P. Balermpas1, M. Guckenberger1, and N. Andratschke1; 1Department of Radiation Oncology, University Hospital Zurich, University of Zurich, Zurich, Switzerland, 2Memorial Sloan Kettering Cancer Center, New York, NY
Purpose/Objective(s): Some patients with non-small cell lung cancer (NSCLC) require a second course of radical thoracic radiotherapy (RT). We compared outcomes and toxicities of NSCLC patients treated with repeat RT, classified as reirradiation (reRT) type 1, type 2, or repeat organ irradiation using the ESTRO/EORTC classification.
Materials/Methods: This retrospective study included NSCLC patients who received a second course of VMAT-based radical thoracic RT (=40 Gy EQD2) between 2015 and 2023. ReRT type 1 involved overlapping irradiated volumes (50% isodose lines). ReRT type 2 had non-overlapping volumes but exceeded cumulative dose constraints, increasing toxicity risks. Other cases were classified as repeat organ irradiation. Time-to-event analysis was performed using the Kaplan-Meier method with log-rank tests for significance. Univariable Cox regression evaluated clinical variables' impact on outcomes. Toxicity was graded per CTCAE v5.0.
Results: Among 150 patients, 72 (48.0%) were classified as reRT type 1, 34 (22.7%) as reRT type 2, and 44 (29.3%) as repeat organ irradiation. Median age was 68 (range 36-87); 93 (62.0%) were male, and 123 (82.0%) were current/former smokers. Adenocarcinoma was the most common histology (n=85, 56.7%). Fifty-six patients (37.3%) received systemic therapy before retreatment, mainly immuno- (n=25, 16.7%) or targeted therapy (n=16, 10.7%), with 48 (32.0%) continuing during/after retreatment. ReRT type 1 was primarily for locoregional recurrences (n=36, 50.0%). ReRT type 2 and repeat organ irradiation targeted metastases more frequently (n=21, 61.8%; n=23, 52.3%), with peripheral lesions being common in both (n=23, 67.6%; n=35, 79.5%), while reRT type 1 was often for central/ultracentral lesions (n=43, 58.4%). After a median follow-up of 41 months, the median overall survival (OS) and progression-free survival (PFS) were 26.4 months (95% CI: 24.02-37.78) and 5.7 months (95% CI 4.0-6.9), respectively, with no significant differences between groups (p=0.49; p=0.56). The rates of freedom from local failure (FFLF) at 1 and 2 years were 72.2% (95% CI 64.7-80.6) and 56.4% (95% CI 47.5-67.0), differing significantly between groups (p=0.043). Repeat organ irradiation was associated with better FFLF compared to reRT type 1 or 2 (HR = .46, 95% CI 0.23-0.91, p=0.026). Longer FFLF correlated with no systemic therapy before retreatment and >1 year since prior RT (HR = 0.42, 95% CI 0.22-0.82, p=0.011; HR = 0.53 95% CI 0.31-0.91, p=0.022), while larger tumors predicted worse FFLF (HR = 3.28, 95% CI 1.79-6.02, p<0.001). Grade 3 or higher toxicities occurred in 11 patients (7.3%), mainly pneumonitis (n=4, 2.7%), more frequently in repeat organ irradiation compared to reRT type 1 (9.1% vs. 0%, p=0.02).
Conclusion: This is the first study comparing outcomes and toxicities of NSCLC patients receiving thoracic reRT type 1, type 2, or repeat organ irradiation per ESTRO/EORTC classification. Differences in toxicity and local control highlight distinct therapeutic challenges.