RADT-08. DOSIMETRIC FEASIBILITY OF DIRECT POST-OPERATIVE MRI-LINAC-BASED STEREOTACTIC RADIOSURGERY FOR RESECTION CAVITIES OF BRAIN METASTASES

Abstract Background Post-operative stereotactic radiosurgery (SRS) of patients with brain metastases single resection cavities is typically planned on a post-recovery MRI, 4-6 weeks after resection. However, meanwhile the intracranial metastasis may (re-)grow, and postponing adjuvant systemic treatment increases chance extracranial progression as well. Anticipating direct post-operative SRS to minimize this interval would enable rapid start therapy. In study, we considered MRI-Linac (MRL) SRS, because possibility execute MRI combined MRL instead two separate systems, improving logistics increasing patient comfort. it unclear whether MRL-based be feasible from dosimetric perspective. This study aims shed light feasibility SRS. METHODS We simulated treatments including thirteen resectable treated fraction CT-Linac (CTL) therefore contoured gross tumor volumes (GTV) compared them GTV. Next, non-coplanar VMAT technique for CTL (ncVMAT) coplanar IMRT (cIMRT), creating three plans per patient: ncVMAT plan cIMRT GTV, current clinical standard. RESULTSCompared GTVs defined 15.5% shrunk by > 2cc, 46% expanded 2cc. Although had lower median gradient index higher V3Gy skin, they were clinically acceptable according guidelines. CONCLUSION slightly inferior plans, dosimetrically acceptable, at trade-off between increased comfort logistics. Additionally, enables substantially earlier therapies, thereby maximizing control.