ESTRO 2025 - Abstract Book

S1405

Clinical - Lung

ESTRO 2025

Conclusion: To our knowledge, this is the first major series in our country involving non-selected patients in real-world daily practice. Although 55Gy/20 has long been considered the standard of care in the United Kingdom, it is not widely established in our country, especially for patients undergoing concomitant chemotherapy. This study provides valuable data and supports the findings of previous publications, presenting an efficient and well-tolerated treatment option, particularly attractive in busy radiation oncology departments.

Keywords: Lung cancer, hypofractionation, radiochemotherapy

References: Maguire, J., Khan, I., McMenemin, R., O'Rourke, N., McNee, S., Kelly, V., Peedell, C., & Snee, M. (2014). SOCCAR: A randomised phase II trial comparing sequential versus concurrent chemotherapy and radical hypofractionated radiotherapy in patients with inoperable stage III Non-Small Cell Lung Cancer and good performance status. European Journal of Cancer, 50 (17), 2939-949. https://doi.org/10.1016/j.ejca.2014.07.009

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Digital Poster Prognostic effect of thoracic radiotherapy dose after chemotherapy in extensive stage small cell lung cancer patients Dilara Ozturk 1 , Cenk Umay 1 , Naciye Sinem Gezer 2 , Caner Ozturk 2 , Busra Tozduman 3 , Gul Ergor 3 , Ayse Nur Demiral 1 1 Radiation Oncology, Dokuz Eylul University, Izmir, Turkey. 2 Radiology, Dokuz Eylul University, Izmir, Turkey. 3 Public Health, Dokuz Eylul University, Izmir, Turkey Purpose/Objective: The effect of increasing the total dose (TD) tBED 10Gy of thoracic-RT (TRT) given after systemic therapy on loco regional (LR) response to RT and survival in patients with ES-SCLC was analyzed. Material/Methods: Between 2009 and 2023, 60 patients with a diagnosis of ES-SCLC who received at least two cycles of induction chemotherapy before TRT in at least 10 fractions or with a TD BED 10Gy of >36Gy were retrospectively evaluated. Time-Adjusted Biological Effective Dose (tBED 10Gy ) formula was used to compare the TDs of different RT fractionation schemes in terms of efficacy. Statistical analysis of the data was performed using SPSS v.26. Chi square test and logistic regression analysis were used to evaluate the factors affecting LR response after TRT. Kaplan-Meier method was used to calculate survival rates. Log-rank test and Cox regression analysis were performed to evaluate the effect of prognostic factors on survival. Results: Median follow-up was 7.5(1-77) months. Median OS was 15.9 months, 1-year and 2-year OS rates were 73.3% and 24.9%. Median PFS was 8.3 months, 1-year and 2-year PFS rates were 29.3% and 11.8%; median DPFS was 9.4 months, 1-year and 2-year DPFS rates were 37.4% and 15.1%, respectively. Median LRPFS was 19.8 months, and 1 year and 2-year LRPFS rates were 65% and 38.1%. The median TD of TRT was 44(30-70)Gy (tBED 10Gy >50Gy in 24 patients; <50Gy in 36 patients). Multivariate analysis (MVA) of the factors affecting LR response after TRT showed that only stage N0-2 (p:0.044) and tBED 10Gy >50Gy (p:0.031) significantly increased the response. TRT TD tBED 10Gy affected median PFS (p:0.006) and median DPFS (p:0.010) significantly in univariate analysis (UVA), however it lost its significance in MVAs. When tBED 10Gy >50Gy and <50Gy groups were compared by UVA; 1-year OS rates were 87.5% and 63.9% (p:0.049), 1-year PFS rates were 45.8% and 17.6% (p:0.006), 1-year DPFS rates were 50% and 26.5% (p:0.017), and 1-year LRPFS rates were 70.8% and 40.6% (p:0.029), respectively. In MVA, the effect of TRT tBED 10Gy level on 1-year LRPFS lost its significance (p:0.263). In addition, in the subgroup of “patients with CR in distant