S743
Clinical – Lower GI
ESTRO 2026
simultaneous integrated boost (SIB) technique. Material/Methods: This study included 82 patients with LARC treated between June 2020 and April 2022. Radiotherapy was delivered with 45 Gy (1.8 Gy per fraction) to the mesorectum and regional lymphatics, with a SIB to 54 Gy to the primary tumor (2.16 Gy per fraction). Concomitant chemotherapy with 5-fluorouracil and leucovorin was administered during weeks 1 and 5 of radiotherapy. Treatment response was evaluated eight weeks after completion of nCRT using pelvic magnetic resonance imaging (MRI), rigid proctoscopy, and digital rectal examination. Patients achieving a clinical complete response (cCR) with distally located tumors were managed with a W&W approach, while others proceeded to surgery 8–14 weeks post-nCRT. DFI was calculated from the date of surgery or, for W&W patients without relapse, from the date of control MRI to the occurrence of progression or last follow-up. Both pretreatment and post-nCRT parameters were analyzed. Results: The majority of patients had distally located tumors (80.5%) and stage III disease (96.4%). Extramural vascular invasion (EMVI) on baseline MRI was present in one-third of patients. Of the 82 patients, 66 (80.5%) underwent surgery and 16 (19.5%) were managed with W&W. A favorable response, defined as cCR or Mandard tumor regression grade (TRG) 1–2, was observed in 40 patients (48.8%). Local regrowth occurred in seven W&W patients, all successfully salvaged surgically. The median DFI was 33.5 months (range 1–54), with a 3-year DFI rate of 74.8%. Multivariate Cox regression identified mucinous tumor component in the initial biopsy, EMVI positivity on baseline MRI, and poor MRI-based tumor regression (mrTRG 4) after nCRT as independent predictors of shorter DFI.
= 0.055). No significant difference was seen between FOLFOX and FOLFIRI (p = 0.357), though FOLFOX plus EGFR inhibition yielded the best results. Conclusion: SBRT provides excellent local control of liver metastases, particularly in first-line patients with RAS wild-type tumors and those receiving EGFR-targeted agents. RAS mutations were associated with lower CR rates, suggesting potential intrinsic radioresistance. These findings highlight the importance of molecular profiling, treatment sequencing, and strategic integration of SBRT with systemic therapy to maximize local efficacy in metastatic colorectal cancer. Keywords: SBRT Liver Metastases, RAS-status, Systemic Therapy Digital Poster 4817 Identifying high-risk patients after neoadjuvant chemoradiotherapy for rectal cancer: A DFI multivariate prognostic model Mladen Marinkovi ć 1,2 , Suzana Stojanovi ć -Rundi ć 1,2 , Du š ica Gavrilovi ć 3 , Aleksandar Toma š evi ć 1,2 , Radmila Jankovi ć 4 , Ana Djuri ć 4 , Jerome Zoidakis 5,6 , Sergi Castellví-Bel 7 , Remond J A Fijneman 8 , Milena Č avi ć 4 1 Clinic for Radiation Oncology, Institute for Oncology and Radiology of Serbia, Belgrade, Serbia. 2 Faculty of Medicine, University of Belgrade, Belgrade, Serbia. 3 Data Center, Institute for Oncology and Radiology of Serbia, Belgrade, Serbia. 4 Department of Experimental Oncology, Institute for Oncology and Radiology of Serbia, Belgrade, Serbia. 5 Department of Biotechnology, Biomedical Research Foundation, Academy of Athens, Athens, Greece. 6 Department of Biology, National and Kapodistrian University of Athens, Athens, Greece. 7 Gastroenterology Deparment, Fundació de Recerca Clínic Barcelona- Institut d'Investigacions Biomèdiques August Pi i Sunyer, Centro de Investigación Biomédica en Red de Enfermedades Hepáticas y Digestivas, Clínic Barcelona, University of Barcelona, Barcelona, Spain. 8 Department of Pathology, The Netherlands Cancer Institute, Amsterdam, Netherlands Purpose/Objective: The standard treatment for locally advanced rectal cancer (LARC) includes neoadjuvant chemoradiotherapy (nCRT), followed by total mesorectal excision (TME) or a watch-and-wait (W&W) approach in selected cases. Identifying reliable prognostic markers is essential for optimizing treatment strategies and personalizing patient management. This study aimed to determine prognostic parameters associated with the disease- free interval (DFI) in LARC patients treated with volumetric modulated arc therapy (VMAT) using a
Figure 1. Kaplan–Meier curves for DFI.Table 1. Univariate and Multivariate Cox Regression Analyses of Prognostic Factors for DFI.
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