S694
Clinical – Lower GI
ESTRO 2026
between treatment groups, except for treatment verification which was not always performed online during SCRT in the TNT group. Evaluated radiotherapy quality factors did not contribute to the observed difference in LRR between TNT and CRT. Most LRRs occurred within the CTV. References: 1. Jomy J, Sharma R, Lu R, Chen D, Ataalla P, Kaushal S, et al. Clinical impact of radiotherapy quality assurance results in contemporary cancer trials: a systematic review and meta-analysis. Radiotherapy and Oncology. 2025;207:110875. Keywords: Quality, RAPIDO, LRR Early ctDNA dynamics impact in locally advanced rectal cancer: interim analysis of the MOREOVER study Luca Boldrini 1,2 , Carlo Guglielmo Cattaneo 2 , Maria De Bonis 3 , Giuditta Chiloiro 1 , Angela Romano 1 , Giulia Panza 1 , Alessia Perrucci 3 , Michele Kulesko 4 , Angelo Minucci 3 , Luciano Giacò 4 , Matteo Nardini 1 , Lorenzo Placidi 1 , Maria Antonietta Gamabacorta 1,2 1 Dipartimento di diagnostica per immagini e Radioterapia Oncologica, Fondazione Policlinico Universitario “A. Gemelli” IRCCS, Rome, Italy. 2 Dipartimento di diagnostica per immagini e Radioterapia Oncologica, Università Cattolica del Sacro Cuore, Rome, Italy. 3 Diagnostica Molecolare e Digital Poster 1241 Genomica-GStep Core Faclity di Genomica, Fondazione Policlinico Universitario “A. Gemelli” IRCCS, Rome, Italy. 4 Bioinformatics Facility Core Research, Gemelli Science and Technology Park (GSTeP), Fondazione Policlinico Universitario “A. Gemelli” IRCCS, Rome, Italy Purpose/Objective: The MOREOVER study investigates whether integrating multi-omics information (radiomics, gut microbiota, and circulating tumor DNA – ctDNA) can improve the prediction of pathological complete response (pCR) in locally advanced rectal cancer (LARC) treated with MRIgRT neoadjuvant chemoradiotherapy (nCRT). This interim analysis reports ctDNA kinetics in a first cohort of ten patients, exploring the relationship between ctDNA dynamics, treatment response and the impact of radiotherapy boost in patients predicted as non- responders to the treatment. Material/Methods: Ten consecutive patients underwent standard nCRT within the THUNDER-2 trial (NCT04815694). Liquid biopsies were collected at three timepoints: before nCRT (T1), at 22 Gy (T2), and before surgery (T3). ctDNA tumor fraction (%) was quantified by targeted NGS. Data were analyzed for longitudinal variation ( Δ T1–T3), outliers were excluded using the IQR method, and log-
63%) patients, ‘borderline’ in 5 (TNT, 15%) and 4 (CRT, 25%) patients, and ‘out-of-field’ in 2 CRT patients (13%) (Figure 1).
Conclusion: Radiotherapy quality in the RAPIDO trial was similar
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