ESTRO 2025 - Abstract Book

S667

Clinical - CNS

ESTRO 2025

1 Department of Radiation Oncology, Peter MacCallum Cancer Centre, Melbourne, Australia. 2 Department of Radiation Oncology, Inselspital, Bern University Hospital, University of Bern, Bern, Switzerland. 3 Sir Peter MacCallum Department of Oncology, The University of Melbourne, Melbourne, Australia. 4 Department of Neurosurgery, The Royal Melbourne Hospital, Melbourne, Australia Purpose/Objective: The biologically optimal time for brain metastasis (BrM) resection after pre-operative stereotactic radiosurgery (preSRS) is unclear. Emerging data suggests an immunological benefit with a longer interval to resection after preSRS. We conducted the first clinical trial to evaluate the feasibility of planned delayed resection (7-21 days) after preSRS. Material/Methods: In this prospective single-centre, single-arm trial, patients with suspected BrMs suitable for preSRS and surgery were eligible. Surgery was scheduled 7-21 days after completion of preSRS (LINAC or GammaKnife-based) where possible. All patients referred to our neurosurgery service and multi-disciplinary meetings for suspected BrMs were screened. The primary endpoint was feasibility of delayed BrM resection after preSRS. Target accrual was 15 patients and the pre-defined feasibility threshold was ten patients (66%) receiving resection 7-21 days after preSRS completion. Secondary endpoints included adverse events (AEs), 6-month local control, and volume change following preSRS. Results: Between 01/2023 and 08/2024, 78 patients for resection of suspected BrMs were screened. The accrual target of 15 patients was met. Common reasons for preSRS ineligibility were lack of existing cancer diagnosis (44%) and size of tumour/peri-tumoural oedema (18%). Two patients refused surgery after preSRS. 14 brain lesions were resected, most commonly of melanoma histology (31%). Median lesion diameter and volume were 25mm (range 15-56mm) and 10.4cc (range 3.0-53.3cc). The most common dose-fractionation was 27Gy in 3 fractions (31%) and 81% of patients received fractionated preSRS. Median time from preSRS completion to resection was seven days (range 0–15 days). Nine lesions in eight patients (56%) were resected 7–21 days after preSRS. Reasons for earlier resection were logistical (n=2), miscellaneous surgeon/patient preferences (n=2), and medical (n=1, to expedite systemic therapy start). No histopathological diagnosis issues were encountered with delayed resection. At time of write-up, 12 patients had completed 6 months follow-up with no BrM local failure. Most common Grade 1-2 AEs were headache and fatigue (20% each), with no Grade >2 AEs. A mean reduction of 21% in lesion volume was observed between preSRS and neurosurgical planning MRIs, correlating with increasing interval between scans (p=0.05). Conclusion: The pre-defined feasibility criterion for delayed resection after preSRS was not met, primarily due to logistical and preferential rather than medical reasons. Still, delayed resection was possible in more than half of patients with no early safety concerns. From an accrual perspective, lack of pre-existing cancer diagnosis was the predominant reason for preSRS non-suitability. A translational sub-analysis will follow.

Keywords: preoperative SRS, brain metastases