2259 - CBCT Based Online Adaptive Radiotherapy (oART) of Locally Advanced Rectal Cancer (LARC) - First Clinical Experience and Dosimetry Benefits: A Prospective Observational Study

03:00pm - 04:00pm ET

Poster Hall - Exhibit Hall A

Screen: 19

POSTER

Presenter(s)

Natalia Wisniewska, MD - Lower Silesian Oncology, Pulmonology and Hematology Center, Wroclaw, -1

N. Wisniewska¹, A. Sztuder^1,2, M. Janiszewska³, and A. Maciejczyk^4,5; ¹Lower Silesian Oncology, Pulmonology and Hematology Center, Wroclaw, Poland, ²Department of Oncology, Medical University of Wroclaw, Wroclaw, Poland, ³DCOPiH, Wroclaw, Dolnoslask, Poland, ⁴Lower Silesian Oncology, Pulmonology and Hematology Center, Wroclaw, Poland, ⁵Department of Oncology, Medical University of Wroclaw, Wroclaw, Poland

Purpose/Objective(s):

Radiation therapy (RT) plays a key role in the management of LARC. Current guidelines recommend several possible sequences of therapy, depending on clinical stage, defining tumor location, and CRM status. Polish diagnostic and treatment guidelines with contributions from experts recommend the use of short-course RT with or without chemotherapy (CTH) in the neoadjuvant setting. To provide both optimal and comprehensive management of RC, the multidisciplinary team’s expertise is crucial. There is a need for standardized OAR delineation and toxicity correlated with normal tissue dose-volume histograms (DVH) consensus. oART uses artificial intelligence to adjust the treatment to the anatomy of the day. This study will provide updated dosimetric results and evaluate toxicity and treatment response using daily oART on the Ethos™ platform for LARC.

Materials/Methods:

The primary endpoint is assessment of the frequency and severity in the incidence CTCAE v. 5 acute treatment-related GI and bladder toxicity according to change in tumor and OAR position and volume during RT correlated with normal tissue DVH, risk stratification for oncological treatment for patients with comorbidities according to CCI. Secondary endpoints include: QoL, dosimetric quality, clinical and pathological response, 2-year LC, identifying challenges, and optimization in the adaptive workflow. 31 patients with biopsy-verified adenocarcinoma with LARC suitable for preoperative short-course (5x5Gy) RT, comparing dosimetric data from scheduled and adapted treatment IMRT plans, were analyzed. 16 Patients received sequential neoadjuvant CTH. Surgical resection was performed in a group of 17 Patients. Toxicity and QoL were reported with CTCAE, PROMs.

Results:

Accrual began in May 2025 and is expected to finish in May 2027. Primary endpoint results are expected to be available in September 2027. Acute Grade =3 treatment related toxicities occurred in 1 (3%) patient and acute =2 in 5 (16%) patients. A clinical major response was achieved in 6 (35%) patients, including 3 (18%) who had a complete clinical response. A pathological major response was achieved in 10 (59%) patients, including 7 (41%) who had a complete pathological response. We produced plans, all fulfilling target coverage criteria. Mean oART CTV coverage 99-100% and mean oART PTV coverage 99% with least doses at OARs.

Conclusion:

This is the first study utilizing preoperative oART to treat LARC. We hope to determine whether there is a clinical and dosimetric benefit for the patients, with analize acute GI and bladder toxicity without compromising treatment efficacy and design implementation widespread protocol for this novel RT technology.