S987
Clinical - Oligometastatic cancer
ESTRO 2026
patient selection for repeated SBRT remains limited. This study evaluated outcomes of patients who underwent ≥ 2 sequential courses of SBRT for OMD, stratified by OMD classification. Material/Methods: Patients receiving two or more separate SBRT courses for ≤ 5 colorectal metastases between 2015 and 2022 at a Dutch academic hospital were retrospectively included. SBRT was delivered at ablative doses (biological equivalent dose (BED) > 100 Gy, a/b=5). Repeated SBRT was defined as a subsequent course for new, progressing, or persistent limited metastases, during a treatment-free interval or ongoing systemic therapy. Patient, tumor, and treatment characteristics were extracted from medical records. Overall survival (OS) and systemic therapy–free survival (STFS) from first and second SBRT were assessed using Kaplan- Meier methods and compared between genuine and induced OMD using log-rank tests. Results: Among 44 patients, 25 had genuine OMD and 19 induced OMD at first SBRT.The lung was the most frequently treated site at both first (50%) and second SBRT (51%). Lymph nodes were the second most common at first SBRT (25%), while bone metastases were the second most common at second SBRT (20%). Median follow-up from second SBRT was 38.7 months (95% CI, 17.7–NR), and median time between first and second SBRT was 13.6 months (IQR 8.8–30.1). Prior to first SBRT, 72.7% had received other metastasis- directed therapies, and 47.7% received systemic therapy for metastatic CRC. Median OS from first SBRT was 49.3 months for genuine OMD vs. 56.0 months for induced OMD (p=0.67); from second SBRT, 27.4 months for genuine vs. 37.1 months for induced OMD (p=0.94). Median STFS from first SBRT was not reached for genuine vs. 27.2 months for induced OMD (p=0.054); from second SBRT, not reached for genuine vs. 13.0 months for induced OMD (p=0.083). Conclusion: Repeated SBRT for recurrent oligometastatic CRC provides durable disease control and survival. Comparable OS was found for genuine and induced OMD, though STFS is shorter in induced OMD. This supports repeated SBRT as a feasible strategy in selected patients. A retrospective, international, multicentre study is ongoing to evaluate outcomes of SBRT in combination with other repeat local therapies in oligometastatic CRC. References: [1] Guckenberger M, Lievens Y, Bouma AB, et al. Characterisation and classification of oligometastatic disease: a European Society for Radiotherapy and Oncology and European Organisation for Research and Treatment of Cancer consensus recommendation. Lancet Oncol. 2020;21(1):e18-28. doi:10.1016/S1470- 2045(19)30718-1.
Conclusion: This study, with one of the longest radiological follow- ups after adrenal SABR, demonstrates durable control and frequent early regression, but also late recurrences. Transient interfraction and early post- treatment changes failed to predict late outcomes, underscoring the need for long-term imaging and better predictive biomarkers. References: 1Giraud N, Schneiders FL, Van Sornsen De Koste JR, Palacios MA, Senan S. Tumor volume changes during stereotactic ablative radiotherapy for adrenal gland metastases under MRI guidance. Radiother Oncol 2023;186:109749. https://doi.org/10.1016/j.radonc.2023.109749. Keywords: Adrenal metastases; MR-SABR Digital Poster 4224 Outcomes after repeated stereotactic body radiotherapy for oligometastatic colorectal cancer Dania Al-Toma 1 , Marie-Christine E. Bakker 2 , Martijn P.W. Intven 3 , Guus M. Bol 2,4 1 Department of Radiology and Nuclear Medicine, University Medical Center Utrecht, Utrecht, Netherlands. 2 Department of Medical Oncology, University Medical Center Utrecht, Utrecht, Netherlands. 3 Department of Radiation Oncology, University Medical Center Utrecht, Utrecht, Netherlands. 4 Division of Hematology & Oncology, Department of Medicine, University of California, San Francisco, San Francisco, USA Purpose/Objective: Oligometastatic colorectal cancer (CRC) can be treated with local therapies such as stereotactic body radiotherapy (SBRT). Patients with oligometastatic disease (OMD) can be classified as genuine OMD (no prior polymetastatic history) or induced OMD (history of polymetastatic disease). [1] Some patients experience recurrent OMD episodes, enabling repeated SBRT. Evidence on the efficacy and optimal
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