ESTRO 2024 - Abstract Book

S1483

Clinical - Lower GI

ESTRO 2024

The lack of survival advantage in the NK cohort is likely be due to the low numbers receiving this treatment and/or due to the high use of neo-adjuvant LCRT.

Keywords: rectal, adjuvant, chemotherapy

References:

[1] Bahadoer, RR et al. Lancet Oncol. 2021,22(1):29-42. https://doi.org/10/1016/S1470-2045(20)30555-6.

[2] Conroy, T et al. Lancet Oncol 2021;22:702-15. https://doi.org/10/1016/S1470-2045(21)00079-6

445

Proffered Paper

Acute toxicity after 3D-CRT versus IMRT/VMAT for locally advanced rectal cancer in the RAPIDO trial

Max D Tanaka 1 , Bengt Glimelius 2 , Geke A.P. Hospers 3 , Elma Meershoek Klein-Kranenbarg 4 , Corrie A.M. Marijnen 1,5 , Annet G.H. Roodvoets 4 , Cornelis J.H. van de Velde 4 , Boudewijn van Etten 6 , Per J Nilsson 7 , Alice M. Couwenberg 1 1 The Netherlands Cancer Institute, Department of Radiation Oncology, Amsterdam, Netherlands. 2 Uppsala University, Department of Immunology, Genetics and Pathology, Uppsala, Sweden. 3 University Medical Center Groningen, Department of Medical Oncology, Groningen, Netherlands. 4 Leiden University Medical Center, Department of Surgery, Leiden, Netherlands. 5 Leiden University Medical Center, Department of Radiation Oncology, Leiden, Netherlands. 6 University Medical Center Groningen, Department of Surgery, Groningen, Netherlands. 7 Karolinska Institutet, Department of Molecular Medicine and Surgery, Stockholm, Sweden

Purpose/Objective:

Several studies have shown a reduction in toxicity outcomes after treatment of locally advanced rectal cancer (LARC) with intensity-modulated radiotherapy (IMRT) or volumetric modulated arc therapy (VMAT) compared with conventional three-dimensional conformal radiotherapy (3D-CRT). However, these studies are based on retrospective datasets. In addition, data on patients treated with total neoadjuvant therapy (TNT) are lacking. The purpose of this study was to compare preoperative acute toxicity between 3D-CRT and IMRT/VMAT in LARC using prospectively collected data from the international phase III multicenter RAPIDO trial.

Material/Methods:

Patients with LARC and at least one high-risk factor (cT4, cN2, extramural vascular invasion, involved mesorectal fascia or enlarged lateral lymph nodes) were enrolled from 2011 to 2016 in seven countries. Patients in the experimental (EXP) arm received short-course radiotherapy (5x5 Gy) followed by chemotherapy (6 cycles CAPOX or 9 cycles FOLFOX4) and in the standard (STD) arm chemoradiotherapy (25-28 x 2-1.8 Gy with twice-daily capecitabine 825mg/m2) optionally followed by postoperative chemotherapy. The CTV was predefined in the study protocol and included at least the mesorectum with the presacral and lateral lymph node stations. Radiation