Objective: To identify factors associated with tumor progression after SRS of the resection bed of a brain metastasis. In addition, we sought to evaluate patterns of failure for patients who eventually had tumor progression.
Methods: We performed a retrospective analysis of 120 patients who underwent tumor bed radiosurgery after an initial gross total resection. The mean imaging follow-up time was 55 weeks. The median margin dose was 16 Gy. Forty-seven patients (39.2%) underwent whole brain radiation therapy (WBRT) before or shortly after SRS.
Results: Local tumor control was achieved in 103 patients (85.8%). Progression-free survival (PFS) was 96% at 6 months, 87 % at 12 months, and 74% at 24 months. Recurrence most commonly occurred deep in the cavity (65%) outside the planned treatment volume (PTV) margin (53%). PTV, cavity diameter, and a margin dose <16 Gy significantly correlated with local failure. For patients with PTVs >=8.0 cc, local PFS declined to 93% at 6 months, 83% at 12 months, and 65% at 24 months. Development or progression of distant metastases occurred in 40% of patients. WBRT was not associated with improved local control.
Conclusion: Resection bed SRS for brain metastases provided excellent local control. The cavity PTV is predictive of tumor control. Because failure usually occurs outside the PTV, inclusion of a judicious 2-3 mm margin beyond the area of post-operative enhancement may be prudent.
From: Predicting Tumor Control after Resection Bed Radiosurgery of Brain Metastases by Luther et al.