ESTRO 2021 Abstract Book

S981

ESTRO 2021

patients with grade 3 and higher radiation pneumonia (RP) compared to patients without RP. As the irradiated lung V5 and V20 volume percentages increased, miRNA-155 expression level decreased after treatment (p = 0.03, 0.01). Post-treatment miRNA-21 expression level was statistically lower in patients with a partial response despite stable disease or progression (p = 0.05). Conclusion Our study is the first study evaluating the relationship of miRNA-21 and miRNA-155 with acute adverse effects and early tumor response in NSCLC treated with definitive CRT. It is thought that miRNA-21/155 may be a biomarker in predicting acute side effects, especially miRNA-155 has predictive value to show radiation- induced lung damage. To understand the role of miRNAs in the development of acute side effects and to be a biomarker, long-term studies with a larger scale are needed. PO-1183 Mean heart dose predicts survival of NSCLC patients treated with chemoradiotherapy and durvalumab E. Ćirić 1 , S. Jelerčič 1 , M. Vrankar 1 , J. But Hadžić 1 , K. Stanič 1 , A.L. Vodušek 1 1 Institute of Oncology Ljubljana, Radiation Oncology Department, Ljubljana, Slovenia Purpose or Objective Since the results of PACIFIC trial, consolidation treatment with durvalumab has become the standard of care for patients with stage III unresectable non-small cell lung cancer (NSCLC) with response to chemoradiotherapy (CRT). First reports show comparable efficacy and toxicity of this treatment strategy in the real-life setting. The data on factors predicting survival of these patients is however scarce. Materials and Methods In this retrospective analysis we reviewed patients with stage III NSCLC and disease control after CRT who were included in durvalumab early access programme in Slovenia. Survival curves were estimated using the Kaplan-Meier method. Cox regression model was used for multivariate analysis to evaluate the effect of different prognostic factors including radiotherapy parameters. Results A total of 59 patients were included, median age 62 years (36-73), 71.2% were male, 78.0% in stage IIIB or IIIC and 96.6% had ECOG 0-1. 66.1% had squamous-cell carcinoma and 30.5% adenocarcinoma. PD-L1 expression was 0% in 22.0%, ≥1% in 66% and unknown in 11.9% of patients. Concurrent chemotherapy was given to 59.3% of patients, sequential to 40.7%. Majority of patients (86.4%) received a total dose of at least 60Gy. Median follow up period was 28 months. Median post-CRT progression-free survival (PFS) for the entire cohort was 22.6 months and not reached for overall survival (OS). Estimated 12 and 18-month PFS rate were 67.8% and 55.9%, estimated 12 and 18-month OS rate were 84.7% and 72.8%. No patient experienced ≥G3 immune related (IO) toxicity, whereas 47.5% patients experienced G2 or less IO toxicity. Pneumonitis was observed in 9 patients (15.3%). There was no significant difference in PFS or OS in patients with 0% vs ≥1% PD-L1 expression and patients who received concurrent vs. sequential CRT. In the univariate analysis mean heart dose (MHD) was correlated with significantly improved PFS (p=0.023) and PTV volume showed trend toward significance (p=0.076). In the multivariate analysis MHD remained significant with HR 2.11 (95% CI 1.02-4.37), p=0.045. Estimated 12-month PFS rate for patients receiving MHD≤8.5Gy and >8.5Gy was 80.6% and 53.6%.

Conclusion Outcomes of patients in real-life setting are aligned with PACIFIC trial. There might be an association between radiotherapy dose to the heart and survival of patients treated with this combined therapy that warrants further investigation.

PO-1184 Pathological response after neoadjuvant chemotherapy versus chemoradiotherapy in stage III NSCLC