ESTRO 2025 - Abstract Book

S1375

Clinical - Lung

ESTRO 2025

2814

Mini-Oral Impact of Estimated Dose of Radiation to Immune Cells (EDRIC) in Locally Advanced NSCLC: Secondary Analysis of the Randomized PET-Plan Trial Cas Stefaan Dejonckheere 1 , Younèss Nour 1 , Jörg Sahlmann 2 , Michael Tobias Engelhart 3 , Hammi Abdelkhalek 4 , Simeon Ari Barth 5 , Tanja Schimek-Jasch 3 , Sonja Adebahr 3 , Markus Hecht 6 , Cornelius F. Waller 7 , Severin Schmid 8 , Matthias Miederer 9 , Alexander Brose 10 , Harald Binder 2 , Jochem König 11 , Andreas Rimner 3 , Anca-Ligia Grosu 3 , Ursula Nestle 3,12 , Eleni Gkika 3 1 Department of Radiation Oncology, University Hospital Bonn, Bonn, Germany. 2 Institute of Medical Biometry and Statistics, University of Freiburg, Freiburg, Germany. 3 Department of Radiation Oncology, University of Freiburg, Freiburg, Germany. 4 Department of Radiation Oncology, Technical University Dortmund, Dortmund, Germany. 5 Department of Pediatrics, University of Freiburg, Freiburg, Germany. 6 Department of Radiotherapy and Radiation Oncology, Saarland University Medical Center, Homburg, Germany. 7 Department of Medical Oncology, University of Freiburg, Freiburg, Germany. 8 Department of Thoracic Surgery, University of Freiburg, Freiburg, Germany. 9 Department of Translational Imaging in Oncology, University of Technology Dresden, Dresden, Germany. 10 Department of Diagnostic and Interventional Radiology, University Hospital Giessen, Giessen, Germany. 11 Institute of Medical Biostatistics, Epidemiology, and Informatics, University Hospital Mainz, Mainz, Germany. 12 Department of Radiation Oncology, Kliniken Maria Hilf, Mönchengladbach, Germany Purpose/Objective: A higher estimated dose of radiation to immune cells (EDRIC) has been proposed as an explanation for failed attempts at thoracic radiation intensification as a part of concurrent chemoradiotherapy (cCRT) for locally advanced non-small cell lung cancer (NSCLC), as lymphopenia in particular is a negative prognostic factor in this context. We sought to evaluate the impact of EDRIC on local control and survival in this secondary analysis of the prospective PET-Plan trial (ARO-2009-09; NCT00697333). Considering the immune system as an organ at risk is of major importance in the current era of consolidation immunotherapy. Material/Methods: Eligible patients had previously received isotoxically dose-escalated chemoradiotherapy up to 60–74 Gy with radiation treatment planning based on an 18 F-FDG PET/CT targeting all CT positive lymph nodes plus 50 Gy elective nodal irradiation (arm A) versus targeting only PET-positive nodes (arm B). EDRIC was calculated with the original model by Jin et al. in addition to a modified score with cohort-specific weight parameters. Results: Sufficient data were available in 153 patients with a median follow-up time (95% confidence interval [CI]) of 41.6 (34.6−53.7) months. Using the original model, the mean EDRIC (range) was 5.70 (3.23−8.44) Gy and showed a strong inverse correlation with PFS (hazard ratio [HR] = 1.77; 95% CI 1.23–2.54; p = 0.002) and OS (HR = 1.72; 95% CI 1.12– 2.65; p = 0.01). The mean modified EDRIC (range) was 5.30 (3.01−8.38) Gy, again with a strong inverse correlation with PFS (HR = 1.66; 95% CI 1.16–2.38; p = 0.006) but not OS (HR = 1.40; 95% CI 0.91–2.15; p = 0.122). Neither radiation treatment allocation (arm A vs. B) nor technique (3D-CRT vs. IMRT) influenced EDRIC ( p = 0.889 and p = 0.958, respectively) and EDRIC did not influence the rate of early or delayed hematological toxicity. Conclusion: Higher doses of radiation to the immune system were associated with worse PFS in this secondary analysis of the PET-Plan trial. The omission of elective nodal irradiation did not influence EDRIC. Future trials should aim to refine existing models and investigate ways to reduce EDRIC to limit its effects in patients undergoing cCRT for locally advanced NSCLC.

Keywords: NSCLC, concurrent chemoradiotherapy, EDRIC