ESTRO 2025 - Abstract Book

S1184

Clinical – Lower GI

ESTRO 2025

Results: Median follow-up was 49.6 months (IQR:17.6–71.3months). Median age was 73 years (IQR 61–79). Most patients (70.3%) were cT3, 11 (17.2%) were cT2 and 8 (12.5%) were cT4. Twenty-two (34.4%) patients had a negative lymph nodes status and 42 (65.6%) had positive lymph-nodes. Surgery was performed after a median interval of 13 days after the beginning of radiotherapy (IQR 11–90 days). Fifteen (23.4%) patients complete the entire protocol with administration of adjuvant CHT (5-fuorouracil). In acute, GI toxicity G1 was recorded in 10 (15.6%) patients as proctitis and diarrhea, only one had proctitis G3 with fecal-urgency while five (7.8%) patients recorded increased urinary frequency G1 in GU toxicity. Fifteen (23.4%) patients developed chronic proctitis G1. None developed chronic GU toxicity. Late asthenia was recorded in 2 patients(3.1%). None patients developed acute/chronic HT toxicity. Five years local control, disease free survival, overall survival and cancer specific survival were 87.2%, 87%, 60% and 86.2% respectively. Conclusion: SCRT is an effective treatment in patients with LARC especially if not eligible for concomitant or adjuvant CHT. This study provides that even using CTV delineation like LCRT doesn’t cause significant toxicities and leads to excellent results at 5-years of follow up. Comparative studies are necessary to extend this target delineation in clinical practice. Digital Poster Preoperative Immunomodulatory radiotherapy: feasibility, safety, and surgeon reported outcomes Julien Pierrard 1,2 , Laurent Coubeau 3,4 , Lancelot Marique 3 , Lacroix Valérie 5 , Catherine Hubert 3 , Marc Van den Eynde 6,1 , Geneviève Van Ooteghem 2,1 1 MIRO, UCLouvain, Brussels, Belgium. 2 Department of radiotherapy, Cliniques Universitaires Saint-Luc, Brussels, Belgium. 3 Hepatopancreatobiliary Surgery and Liver Transplantation Unit, Cliniques Universitaires Saint-Luc, Brussels, Belgium. 4 Laboratory of Hepato-Gastroenterology, UCLouvain, Brussels, Belgium. 5 Department of Cardiothoracic Surgery, Cliniques Universitaires Saint-Luc, Brussels, Belgium. 6 Department of oncology, Cliniques Universitaires Saint-Luc, Brussels, Belgium Purpose/Objective: The immunomodulatory effects of RT are currently extensively investigated in preclinical studies. Though human studies are essential for understanding how RT may synergize with immunotherapy, potentially converting “cold” tumours into immunotherapy-sensitive ones. Analysing irradiated tumour samples from patients could provide valuable insights into the RT-induced tumour immune environment modifications. However, the impact of this RT on the surgery is unknown, leaving some impediments to clinical research. Keywords: Rectal cancer, short course, CTV 1983

This analysis evaluates the feasibility and safety of a trial investigating pre-operative immunomodulatory RT in colorectal cancer patients.

Material/Methods: MSS colorectal patients were recruited to irradiate either the primary tumour or metastases. Two levels of dose were selected : (1) 3x8Gy onto the primary tumour or the (largest) metastasis (2) 3x2Gy on a second lesion (if multiple metastases). Radical surgery was scheduled 4-8 days after RT. Blood and tumour samples were collected for biomolecular analysis (full protocol in Figure 1).