ESTRO 2025 - Abstract Book

S1770

Clinical – Upper GI

ESTRO 2025

rate, local control (LC), toxicity, distant metastasis-free survival (DMFS), and overall survival (OS) following CHT with anticipated SBRT+CHT in LAPC.

Material/Methods: Using the Gehan design, the study initially enrolled 14 patients. If at least one R0 resection was observed, the enrolment would continue to 25 patients to better estimate R0 resectability. SBRT (30 Gy in 5 fractions) was scheduled between the first and second cycles of CHT, with a minimum of 10 days after the second CHT cycle. CHT continued until week 20 post-SBRT, followed by re-evaluation via contrast-enhanced triphasic CT (tCT), based on RECIST criteria, for potential surgical intervention. Results: The median follow-up and age of the 14 enrolled LAPC patients (2018-2022) were 24 months (range: 8-39) and 69 years (range: 50-84), respectively. Treatment included one cycle of CHT, SBRT (VMAT 30 Gy/5 fx), and five cycles of CHT post-SBRT. CHT regimens were gemcitabine + Nab Paclitaxel (14.2%) and FOLFIRINOX (85.8%). Median tumor diameter and CA19-9 levels pre- and post-treatment were 4.0 cm (range: 2.0-7.0 cm), 270.0 U/ml (range: 0.8-6129.0), and 53.0 U/ml (range: 0.8-278.8), respectively. Outcomes included five partial responses (38.5%), six stable diseases (46.1%), and two progressive diseases (15.4%). The resectability rate was 21.4%, with two R0 and one R1 resections. One case of Grade 3 late toxicity (gastric ulcer) was recorded. Median, 2-year, and 3-year OS, LC, DMFS rates were 24, 20, and 10 months; 38.5%, 36.4%, and 31.3%; 19.2%, 36.4%, and 0.0%, respectively. Median OS was significantly higher in pancreatic body tumors compared to head tumors (38 vs 22 months, p=0.05). Conclusion: Anticipated SBRT in combination with modern CHT regimens appears effective and well-tolerated, enhancing the resectability of unresectable LAPC. With two R0 resections achieved, the study will extend to 25 patients. Digital Poster Image-guided carbon ion stereotactic radiotherapy of hepatocellular carcinoma: paving the way for MR guided online adaptive therapy Sebastian Regnery 1,2,3 , Rita Pestana 1,2,3 , Paula Hoffmeister-Wittmann 4 , Thomas Mielke 2 , Philipp Hoegen Saßmannshausen 1,2,3 , Fabian Weykamp 1,2,3 , Friderike Longarino 1,2,3 , Cedric Beyer 1,2,3 , Jakob Liermann 1,2,3 , Sebastian Klüter 1,2,3 , Jürgen Debus 1,2,3 , Julia Bauer 1,2,3 , Katharina Seidensaal 1,2,3 1 Department of Radiation Oncology, Heidelberg University Hospital, Heidelberg, Germany. 2 Heidelberg Ion Beam Therapy Center (HIT), Heidelberg University Hospital, Heidelberg, Germany. 3 Heidelberg Institute for Radiation Oncology (HIRO), National Center for Radiation Research in Oncology (NCRO), Heidelberg, Germany. 4 Department of Medial Oncology, National Center for Tumor Diseases (NCT), Heidelberg, Germany Purpose/Objective: Stereotactic body radiotherapy (SBRT) has emerged as effective local treatment of hepatocellular carcinoma (HCC) [1-3]. Carbon ion stereotactic radiotherapy (CISR) yields high tumor control and could spare organs-at-risk (OAR) better than photon SBRT [4]. However, CISR is sensitive to interfractional motion. We aim to quantify the dosimetric benefits of daily online adaptive CISR. Material/Methods: We analyzed 13 patients that received 4 x 10.5 Gy (RBE-weighted dose) CISR to 14 HCC lesions in challenging locations (N=10: liver dome, N=3: < 1cm from intestines). All patients underwent daily in-room CT imaging, and four patients were shuttled to an MRI simulator (1.5 Tesla). The baseline plan was re-calculated on daily imaging before Keywords: pancreatic neoplasm, SBRT, chemotherapy 1438