ESTRO 2025 - Abstract Book

S1512

Clinical – Mixed sites & palliation

ESTRO 2025

Material/Methods: This retrospective study at UZ Brussel – follow-up till Jan 2024 – analyzed a cohort of 100 patients with OMD treated with SBRT, between Jul 2012-Feb 2017, delivering 50Gy in 10 fractions on the 80% isodose line. Lesion movement was managed using Internal Target Volume (ITV) or Dynamic Tumor Tracking (DTT) with marker, respectively with peak-to-peak amplitude (PPA) < 7mm or PPA > 7mm. The primary endpoint of the study was long-term LC and finding variables associated with LC using a Cox Proportional-Hazards model. Results: 100 patients were treated for a total of 211 metastatic lesions. Lesions were predominantly in the lungs (74%) and were mainly treated using ITV (89%). The lesions had a median GTV tumor size of 2.5cc. Systemic treatment was administered before SBRT in 85% of the patients and afterwards in 39% of the patients. LC rates at 1-,3-,5-, and 10 years were 76.5%, 53.8%, 38.1% and 36.3% respectively. (Figure 1) Median LC was observed at 1332 days (at about 3.65 years). Improved LC was observed in locations other than lung and liver (p=0.024) (e.g., located in pleural, subcutaneous, nodular, renal, adrenal and glandular lesions) and increasing age (p<0.010). Worse LC rates were seen in liver lesions (p=0.103) and systemic therapy post-radiotherapy (p<0.001). No significant associations were found with tumor size or tumor motion, nor significant difference between ITV or DTT.

Conclusion: This study found no significant difference in local control (LC) between ITV and DTT, highlighting the importance of effective motion management in maintaining LC for both static and moving targets in OMD. Lesion location, patient age and systemic therapy post-radiotherapy were the significant prognostic factors for LC.

Keywords: oligometastases, SBRT, long-term local control

References: 1. Van den Begin R, Engels B, Boussaer M, Dhont J, Burghelea M, Depuydt T, et al. Motion management during SBRT for oligometastatic cancer: Results of a prospective phase II trial. Radiother Oncol. 2016;119(3):519-24. 2. Stera S, Miebach G, Buergy D, Dreher C, Lohr F, Wurster S, et al. Liver SBRT with active motion-compensation results in excellent local control for liver oligometastases: An outcome analysis of a pooled multi-platform patient cohort. Radiother Oncol. 2021;158:230-6. 3. Yamamoto T, Niibe Y, Aoki M, Shintani T, Yamada K, Kobayashi M, et al. Analyses of the local control of pulmonary Oligometastases after stereotactic body radiotherapy and the impact of local control on survival. BMC Cancer. 2020;20(1):997.