ESTRO 2025 - Abstract Book

S1153

Clinical – Lower GI

ESTRO 2025

Material/Methods: In this prospective cohort study, two groups of rectal cancer patients receiving neoadjuvant chemoradiotherapy were observed. One group received DA plus nutritional supplementation with PD, while the other received only DA, in a period between the start of radiotherapy until surgery. GAT was measured using the CTCAE 5.0 scale, functionality with the ECOG scale, and nutritional status with GLIM criteria. Results: From the fifty-one patients included: 25 were allocated in the PD group and 26 in the DA+PD group. The DA+PD group showed a lower risk of diarrhea midway through radiotherapy [RR of 0.218 (95% CI=0.052–0.923)] as well as at the end of treatment [RR of 0.103 (95% CI=0.020–0.537)]. Also lower risk of rectal mucositis at the end of treatment [RR of 0.405 (95% CI=0.280–0.584)] was seen in these patients. Furthermore, the PD group experienced fewer interruptions in radiotherapy among stage III patients (0% vs. 15.8%, p=0.049) and malnourished patients (0% vs. 18.2%, p=0.040). Conclusion: The glutamine-enriched peptide diet reduced and helped protect against diarrhea and mucositis associated with chemoradiotherapy in rectal cancer patients undergoing neoadjuvant treatment and reduced interruptions in radiotherapy. Digital Poster Where do we stand with the rectal boost RT? A systematic review and meta-analysis Julien Pierrard 1,2 , Geneviève Van Ooteghem 1,2 1 MIRO, UCLouvain, Brussels, Belgium. 2 Department of Radiotherapy, Cliniques Universitaires Saint-Luc, Brussels, Belgium Purpose/Objective: Long-course RT combined with chemotherapy is recommended as total neoadjuvant therapy in locally advanced rectal cancer (LARC) [1]. Non-operative strategies are currently under investigation to propose organ preservation (Watch-and-wait) [2]. Administering an RT boost to the primary tumour during long-course RT may enhance complete response rates, potentially leading to increased organ preservation [3]. However, there is no consensus on how to deliver this boost with external beam RT. This systematic review aims to describe the RT parameters used for delivering a RT boost to the primary tumour in LARC. A meta-analysis was conducted to identify which parameters are associated with improved oncological outcomes. Material/Methods: PubMed and EMBASE were searched from January 2000 to June 2024 using combinations of the terms: “Rectum”, “Radiotherapy”, “Boost”, and related synonyms. In-silico , retrospective and prospective studies involving human with LARC treated with neoadjuvant RT that mentioned the use of a RT boost were included. Study quality was assessed using a modified Newcastle-Ottawa Scale. For the descriptive analysis, data publication characteristics, RT techniques, RT preparation, boost delineation, RT dose, chemotherapy, and follow-up were extracted. The primary endpoints of the meta-analysis were the pathological complete response (pCR) rate for studies involving planned surgery, and the clinical complete response (cCR) rate for Watch-and-Wait studies. The secondary endpoint was the local recurrence rate (LRR). A mixed-effects model was used to pool the effects. Keywords: Rectal-Cancer, toxicity, peptide-diet 323