ESTRO 2025 - Abstract Book

S1741

Clinical – Upper GI

ESTRO 2025

From June 2017 to December 2022, a total of 128 patients with 162 pathologically confirmed positive LNs were included. The study found that LNs in different regions of the same patient responded differently to NCRT. Among all LNs, 35.8% (58/162) achieved pathological complete response (pCR), with the highest pCR rate in the right upper paratracheal lymph nodes (47.8%, 21/44) and an MPR rate of 59.1% (26/44). In the predictive models for LN treatment response, the AUC values for the DL model, Rad model, and DL + Rad model in the test cohort were 0.752, 0.734, and 0.839, respectively. The sensitivities were 0.833, 0.625, and 0.833, and the specificities were 0.348, 0.652, and 0.565, respectively. The DL + Rad model demonstrated better calibration and clinical utility in both the training and test cohorts. Conclusion: Among the three models developed, the DL + Rad model showed the best performance in predicting LN-MPR. This model shows promise for future clinical application to help clinicians evaluate the treatment sensitivity of LNs in different regions after NCRT. References: [1]Yehan Z, Ying L, Peng G, et al. Prognostic significance of positive lymph node regression grade to neoadjuvant chemoradiation for esophageal squamous cell carcinoma [J]. J Surg Oncol, 2024, 129(4): 708-717. [2]Hagi T, Makino T, Yamasaki M, et al. Pathological Regression of Lymph Nodes Better Predicts Long-term Survival in Esophageal Cancer Patients Undergoing Neoadjuvant Chemotherapy Followed by Surgery [J]. Ann Surg, 2022, 275(6): 1121-1129. [3]Zhang S, Tang B, Yu M, et al. Development and Validation of a Radiomics Model Based on Lymph-Node Regression Grading After Neoadjuvant Chemoradiotherapy in Locally Advanced Rectal Cancer [J]. International Journal of Radiation Oncology, Biology, Physics, 2023, 117(4): 821-833. Digital Poster Stereotactic-Ablative-Radiotherapy with Standard LINAC in Locally-Advanced-Pancreatic-Cancer: Resectability and Histopathological-Results Barbara G Salas-Salas 1 , Laura Ferrera-Alayón 1 , Antonio A Alayón-Afonso 1 , Alberto Espinosa-Lopez 2 , Andres Vera Rosas 1 , Gabriel Garcia-Plaza 3 , María L Pérez- Rodríguez 1 , Marta Lloret Saez-Bravo 1 , Pedro Carlos Lara 4 1 Radiation Oncology, University Hospital Dr Negrin, Las Palmas de Gran Canaria, Spain. 2 Radiation Oncology, University Hospital Virgen de la Arrixaca, Murcia, Spain. 3 Hepatic and Pancreatobiliary Surgery Unit, Complejo Hospitalario Universitario Insular Materno Infantil de Gran Canaria, Las Palmas de Gran Canaria, Spain. 4 Department of Oncology, University Hospital San Roque, Las Palmas de Gran Canaria, Spain Purpose/Objective: We have been able to demonstrate, for the first time, the safety and feasibility of escaling up to 55 Gy in 5 fractions (11 Gy/fraction) in borderline (BRPC) or locally advanced unresectable pancreatic cancer (LAPC) using the standard LINAC platform (10.1016/j.ctro.2024.100753). The main purpose of the present study is to evaluate the impact of such neoadjuvant high-dose stereotactic ablative radiotherapy (SABR) on oncological outcomes. Material/Methods: From June 2017-December 2022,patients diagnosed with BRPC/LAPC were treated with neoadjuvant chemotherapy (ChT) and SABR with escalated-dose simultaneous integrated boost(SIB) of 45Gy, 50Gy up to 55Gy (BED ≥100). Radiological evaluation was performed with computed tomography(CT) scan at 6-8weeks post-treatment to determine resectability status, based on established criteria (SAR/APA 2014). Surgical decisions were made by a multidisciplinary tumour board of the participating institutions. Keywords: Esophageal carcinoma; Predicting LN response; 295