ESTRO 2024 - Abstract Book

S1540

Clinical - Lower GI

ESTRO 2024

Results:

the results of 800 patients are herein reported. Patients were treated with concomitant RCHT with (465) or without (335) a RT boost. Dose boost range was 53.8-56 Gy. Patients were operated on after a median time of 9.7 weeks (IQ range 5-24). The median follow-up was 55 months. The overall pCR rate was 22.4% (179 patients). In the subgroup analysis pCR was 29.2% (98) and 16.1% (75) in the boost and no-boost group, respectively (p=0.00). The pCR rate stratified by interval to surgery (≤7, 8-10, 11-12, ≥13) was: 11.8%, 23.1%, 22.6%, 33.1%. In the subgroup analysis, the pCR stratified by interval to surgery was: 11.8%, 23.1%, 22.6%, 33.1% (p=0.27), and 12.2%, 19.9%, 15.4%, 20.7% (p=0.000) for boost and no-boost group, respectively, and the 95% of pCRs occurred within week 16 in the boost group and week 21 in the no-boost group (p=0.000). In the univariate analysis (UVA), patients treated with boost had a higher rate grade 3 or higher acute gastrointestinal (6.3% versus 1.5%; p=0.000) and genitourinary toxicity (5.1% versus 1.4%; p=0.01). Globally, local relapse occurred in 74 patients (9.2%) and the 5 year local relapse-free survival rate was 88.3%. The pCR was associated with an improved local control in the UVA (5-year 95% versus 85.7%; p=0.001). The median OS was 12.8 years, and the 5-year OS was 77%. In the univariate analysis RT boost did not correlate with survival (p=0.18), but having a pCR did (5-year OS: 94.2% versus 72.9%; p=<0.000), as well as baseline staging (p=0.000) and pathological stage (p=0.000). The 5-year metastases-free survival was 73.2%.

Conclusion:

the results of the present study suggest that RT dose-intensified regimens in LARC might significantly increase pCR rate, even if at the cost of higher acute toxicity. While pCR seems only partially improved by prolonged time to surgery in the no-boost group, a progressive and significant pCR improvement in patients treated with boost over time was observed.

Keywords: Rectal cancer, radiochemotherapy

2285

Digital Poster

One year follow-up of total neoadjuvant treatment of rectal cancer by MRI-guided radiotherapy

Mark De Ridder 1 , Jacques Bodenstein Bezuidenhout 1 , Koen Kortbeek 2 , Jens Van Loon 1 , Nele Platteaux 1 , Tim Everaert 1 , Anne-Sophie Bom 1 , Ellen Van Eetvelde 3 , Alexandra Sermeus 4 , Amy de Haar-Holleman 2 , Bente Van der Steen 1 , Camille Raets 1 , Kurt Barbé 1 , Inès Dufait 1 , Sven Van Laere 1 , Thierry Gevaert 1 1 UZ Brussel, VUB, Radiotherapy, Brussels, Belgium. 2 UZ Brussel, VUB, Medical Oncology, Brussels, Belgium. 3 UZ Brussel, VUB, Surgery, Brussels, Belgium. 4 UZ Brussel, VUB, Gastroenterology, Brussels, Belgium

Purpose/Objective:

Currently, total neoadjuvant therapy (TNT) stands as the gold standard for treating locally advanced rectal cancer. The pivotal 'Rectal cancer And Preoperative Induction therapy followed by Dedicated Operation (RAPIDO) trial' by Bahadoer et al. (1) demonstrated a significant decrease in disease-related treatment failure when short-course radiotherapy (5 x 5 Gy) followed by chemotherapy preceded total mesorectal excision (TME). Recent findings from