ESTRO 2025 - Abstract Book

Brachytherapy - Gastro-intestinal, paediatric brachytherapy, miscellaneous

S174

ESTRO 2025

148

Digital Poster Interventional radiotherapy (I-RT) for liver oligometastatic disease from colorectal cancer - a single institution retrospective analysis Mateusz Bilski 1,2,3 , Katarzyna Korab 4 , Magdalena Orzechowska 5 , Julia Ponikowska 4 , Paweł Cisek 6,7 , Jacek Fijuth 8,9 , Łukasz Kuncman 8,9 1 Brachytherapy Department, Saint John's Cancer Center, Lublin, Poland. 2 Radiotherapy Department, Saint John's Cancer Center, Lublin, Poland. 3 Radiotherapy Department, Medical University of Lublin, Lublin, Poland. 4 Department of Medical Physics, Saint John’s Cancer Center, Lublin, Poland. 5 Department of Molecular Carcinogenesis, Medical University of Lódź, Łódź, Poland. 6 Department of Brachytherapy, Saint John’s Cancer Center, Lublin, Poland. 7 Department of Radiotherapy, Medical University of Lublin, Lublin, Poland. 8 Department of Radiotherapy, Medical University of Lódź, Łódź, Poland. 9 Department of External Beam Radiotherapy, opernicus Memorial Hospital in Lodz Comprehensive Cancer Center and Traumatology, Łódź, Poland Purpose/Objective: The standard treatment for oligometastatic (OM) colorectal cancer is systemic therapy +/—surgery +/—metastasis directed therapy (MDT). The best precise strategy to treat those patients is unknown. Brachytherapy/ interventional radiotherapy used as MDT aims to prolong the time to polimetastatic progression and maintain the patient's quality of life and good liver function before future possible lines of systemic therapy. We report outcomes of patients after liver brachytherapy/interventional radiotherapy because of oligometastatic colorectal cancer localized in the liver. Material/Methods: Patients with oligometastatic colorectal cancer with liver metastases were qualified for the analysis. Up to 5 liver metastases were allowed. Single fractions of 15 Gy, 20 Gy, or 25 Gy were used. Starting six months after brachytherapy, patients were followed with serial imaging and evaluated for objective response rate (ORR), disease control rate (DCR), progression-free survival (PFS), and overall survival (OS). PFS and OS were counted from the day of brachytherapy. Overall, 127 patients were included, with 48.8 % of women (n=62), a median age of 65 years, and an ECOG-PS ≤ 2 in all cases. Seventy-three patients had wild-type KRAS gene. One, 2,3, and 4 liver metastases were diagnosed in 29.1 %, 42.5 %, 21.2 %, and 7.1 %, respectively. The median total volume of liver metastases was 128 (2-1372) cc. A median of 3 (1-8) applicators was used. Doses of 15 Gy, 20 Gy, and 25 Gy were prescribed in 29.9 %, 41.7 %, and 28.3 % of patients, respectively. At the 6 th -month imaging analysis, according to RECIST 1.1, the objective response and disease control rates were 22.8 % and 76.4 %, respectively. The median PFS was 9 (2-24) months. Median OS was 16 (4-36) months. Median 1y- and 2y OS were 65 % and 16 %, respectively. Conclusion: Brachytherapy/ interventional radiotherapy in colorectal cancer patients can result in favorable treatment outcomes. It is an alternative radiotherapy modality in the modern era of metastasis-directed therapy for oligometastatic disease. It can prolong the progression-free survival of patients, aiming to preserve normal liver function before future lines of systemic therapy. Results:

Keywords: liver metastases, colorectal cancer, brachytherapy