ESTRO 2025 - Abstract Book

S1792

Clinical – Upper GI

ESTRO 2025

2149

Poster Discussion CBCT-based online adaptive radiotherapy of esophageal cancer in the neoadjuvant setting: dosimetric analysis, toxicity and treatment response Nicolas Bachmann 1 , Maiwand Ahmadsei 1,2 , Moritz Hürlimann 1 , Hubert S. Gabrys 2 , Daniel Schmidhalter 3 , Jenny Bertholet 3 , Martin D. Berger 4 , Yves Borbély 5 , Ekin Ermiş 1 , Emanuel Stutz 1 , Binaya K. Shrestha 1 , Daniel M. Aebersold 1 , Peter Manser 3 , Hossein Hemmatazad 1 1 Department of Radiation Oncology, Inselspital, Bern University Hospital, University of Bern, Bern, Switzerland. 2 Department of Radiation Oncology, Zurich University Hospital, University of Zurich, Zurich, Switzerland. 3 Division of Medical Radiation Physics and Department of Radiation Oncology, Inselspital, Bern University Hospital, University of Bern, Bern, Switzerland. 4 Department of Medical Oncology, Inselspital, Bern University Hospital, University of Bern, Bern, Switzerland. 5 Department of Visceral Surgery and Medicine, Inselspital, Bern University Hospital, University of Bern, Bern, Switzerland Purpose/Objective: Preoperative chemoradiotherapy (CRT) followed by surgery is a treatment option for esophageal cancer (EC). However, concerns persist regarding cardiopulmonary toxicities and inconsistent daily target coverage due to anatomical changes between treatment fractions. To address these issues, we implemented a CBCT-based online adaptive radiotherapy (oART) workflow and demonstrated its feasibility and dosimetric benefits for EC. 1 This study presents updated dosimetric results and assesses toxicity and treatment response of neoadjuvant CBCT-based oART in EC on the Ethos platform . Material/Methods: We analyzed 26 patients with EC (25 adenocarcinomas, AC, 1 squamous cell carcinoma) who underwent neoadjuvant CBCT-based oART, receiving 50.4 Gy in 28 fractions combined with weekly carboplatin and paclitaxel. We documented the mean heart dose, lung V20Gy, and target volume doses for both the scheduled and adapted treatment plans, and assessed differences using box plots and Wilcoxon signed-rank tests. Esophagectomy was carried out 8-12 weeks post-CRT, with treatment response evaluated based on Becker tumor regression grading (Grade 1a = pathologic complete response, pCR, and Grade 1a+1b = pathologic major response, pMR). Grade ≥3 toxicities were documented according to CTCAE v5. Associations between target volume parameters, pMR and toxicity were examined through univariate analysis and Mann-Whitney U tests. Results: With the adapted treatment plans, significant improvements in target dose parameters were achieved compared to scheduled treatment plans (Fig. 1). Most notable differences were observed for mean PTV D99% and CTV D99% , with increases of 20.6% (absolute: 15.6%, p < 0.001) and 6.1% (absolute: 5.4%, p < 0.001), respectively. Additionally, mean heart dose was decreased by 3.8% (absolute: 0.8 Gy, p = 0.038), and mean lung V20Gy was reduced by 3.3% (absolute: 0.7%, p = 0.049) with adapted plans (Fig. 1). As detailed in Table 1, acute Grade ≥3 CRT-related toxicities occurred in 7 (27%) patients, and Grade ≥3 post-operative complications in 17 (65.4%) cases. A pCR was achieved in 8 (30.8%) patients and a pMR in 18 (69.2%) patients. No significant association between target dose parameters and toxicity or pMR was found in the univariate analysis.