ESTRO 2025 - Abstract Book

S1183

Clinical – Lower GI

ESTRO 2025

1980

Digital Poster Short course radiotherapy for locally advanced rectal cancer contoured like long course: toxicity profile Margherita Rotondi 1,2 , Giuseppe Facondo 3,2 , Gianluca Vullo 3,2 , Federico Belotti 2 , Silvia Fiorelli 2 , Stefano Mossa 2 , Vitaliana De Sanctis 2 , Mattia Falchetto Osti 2 1 Radiation Oncology, Azienda Sanitaria Universitaria Trieste, Trieste, Italy. 2 Radiation Oncology, Sapienza MP University of Rome, Rome, Italy. 3 Radiation Oncology, Azienda Sanitaria Universitaria Udine, Udine, Italy Purpose/Objective: Short course radiotherapy (SCRT) contouring for locally advanced rectal cancer (LARC) differs from long course radiotherapy (LCRT), especially for pelvic nodes delineation. We retrospectively analysed and reported feasibility and toxicity profile of SCRT, delineated as long-course term in continuous series of patients in terms of acute and late toxicity. Material/Methods: Sixty-four patients affected by LARC were treated from 2008 to 2023 with SCRT, with preoperative SCRT (total dose of 25 Gy/5 fractions) and prior to possible chemotherapy (CHT). Clinical target volumes (CTV) was drawn as standard LCRT including tumor, mesorectal, presacral, obturator nodes, and internal iliac nodes (started L5-S1). In T4 tumors involving anterior structures the external iliac nodes ware included. For low-lying tumors involving the anal canal the inguinal nodes ware included. An isotropic extension of 5–10 mm was generated from the CTV to obtain the planning target volume (PTV). Radiotherapy was delivered using VMAT/IMRT technique on a 6/15 MV linear accelerator (Fig.1). The patient underwent image-guided radiotherapy using a cone-beam computed tomography scanner as daily imaging prior to treatment. Gastrointestinal (GI), genitourinary (GU) and haematological (HT) toxicities were assessed according to the CTCAEv5.0 in acute and late.