ESTRO 2025 - Abstract Book

S1270

Clinical – Lower GI

ESTRO 2025

References: 1. A TCP-based early regression index predicts the pathological response in neo-adjuvant radio-chemotherapy of rectal cancer. Fiorino et al. Radiother Oncol 2018 2. External Validation of Early Regression Index (ERI TCP ) as Predictor of Pathologic Complete Response in Rectal Cancer Using Magnetic Resonance-Guided Radiation Therapy. Cusumano et al. Int J Radiat Oncol Biol Phys. 2020 3. THUNDER 2: THeragnostic Utilities for Neoplastic DisEases of the Rectum by MRI guided radiotherapy. Chiloiro et al. BMC Cancer 2022

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Digital Poster Comparative analysis of acute toxicity in Total Neoadjuvant Therapy for locally advanced rectal cancer using Long-Course vs Short-Course Radiotherapy Gabriel Campos Rivera, Nerea Ugarte Ruiz de Aguirre, YulY C. Ortiz Bautista, Paula Vicente Ruiz, Jonathan Saavedra Bejarano, Carlos Míguez Sanchez Radiation Oncology, Virgen Macarena University Hospital, Seville, Spain Purpose/Objective: To compare the acute toxicities associated with LCRT and SCRT in patients undergoing TNT for locally advanced rectal cancer and determine if baseline characteristics influence toxicity occurrence. Material/Methods: A retrospective study was conducted on 34 patients with locally advanced rectal adenocarcinoma treated between 2022 and 2024 at a single center. The cohort included 23 men and 11 women, with a median age of 61.5 years (range 48–82). Tumor localization was lower rectum (18 patients), middle rectum (6), and upper rectum (10). TNM staging revealed 5 T2, 18 T3, and 11 T4 tumors; nodal involvement was N0 in 4 patients, N1 in 11, and N2 in 19. Patients received either LCRT (28 patients; 46 Gy in 23 fractions with concomitant capecitabine) or SCRT (6 patients; 25 Gy in 5 fractions without chemotherapy). Acute toxicities were graded according to CTCAE v5.0 criteria. Chi square tests were utilized to compare toxicity levels between treatment groups and assess associations with baseline characteristics. Results: The maximum toxicity grades observed were Grade 0 in 5 patients (14.7%), Grade 1 in 13 (38.2%), Grade 2 in 12 (35.3%), and Grade 3 in 4 (11.8%). The most common acute toxicities included proctalgia (55.9%), tenesmus (58.8%), and diarrhea (44.1%); Grade 3 toxicities were infrequent. Comparative analysis revealed no statistically significant differences between the LCRT and SCRT groups in the incidence or severity of specific toxicities such as dysuria, urinary frequency, urgency, rectal bleeding, proctalgia, tenesmus, diarrhea, and radiodermatitis (p > 0.05). Additionally, no significant associations were found between acute toxicity levels and baseline characteristics, including TNM staging, nodal involvement, extramural vascular invasion, or mesorectal fascia involvement. Conclusion: No statistically significant differences in acute toxicity profiles were observed between LCRT and SCRT in patients undergoing TNT for locally advanced rectal cancer. Baseline characteristics did not significantly influence toxicity occurrence. These findings suggest that both LCRT and SCRT are comparable from a toxicity standpoint within TNT protocols. Clinicians can tailor treatment plans based on patient-specific factors without increasing the risk of acute adverse effects.

Keywords: QOL, TNT