Temporal Changes in Brain Metastasis Resection Sites After Adjuvant Gamma Knife Radiosurgery

Overview

This retrospective study evaluated longitudinal changes in postoperative brain metastasis cavity volumes following adjuvant single-fraction or hypofractionated Gamma Knife radiosurgery (GKRS). The analysis of 98 patients demonstrated dynamic cavity volume evolution post-GKRS, influenced by timing, fractionation, and cavity characteristics, with implications for local control.

Background

Brain metastases are common and historically treated with whole brain radiotherapy (WBRT) and surgery, but WBRT is associated with neurocognitive decline. Modern management favors maximal safe resection followed by focal stereotactic radiosurgery (SRS) such as Gamma Knife to preserve cognition while maintaining oncologic outcomes. Postoperative cavities are dynamic targets whose volume changes over time, affecting treatment planning and local control. Understanding cavity volume kinetics after GKRS is critical for optimizing treatment strategies.

Data Highlights

The study included 98 patients with 98 resection cavities treated with adjuvant GKRS between 2011 and 2025. Volumetric analysis was performed using contrast-enhanced MRI at baseline (GKRS planning) and longitudinal follow-up. Fractionation regimens included single-fraction and predominantly three-fraction hypofractionated GKRS. Key variables included cavity volume at GKRS planning (VGK), early postoperative cavity volume, and percent volume change over time relative to VGK. Clinical variables such as Karnofsky Performance Status and time from surgery to GKRS were also recorded.

Key Findings

• Postoperative resection cavities exhibit dynamic volume changes after GKRS, with a general trend toward volume reduction over time but with nonlinear trajectories.
• Timing from surgery to GKRS influences cavity volume evolution, with earlier radiosurgery associated with different cavity dynamics compared to delayed treatment.
• Fractionation strategy (single-fraction vs. hypofractionated GKRS) impacts cavity volume changes and may affect local control outcomes.
• Inclusion of adjacent dura in the treatment target influences baseline cavity volume measurements and subsequent volumetric changes.
• Longitudinal cavity volume monitoring is essential to understand treatment response and optimize radiosurgical planning.

Clinical Implications

Clinicians should recognize that postoperative brain metastasis cavities are dynamic and their volumes can change significantly between surgery and radiosurgery, as well as during follow-up. Individualizing the timing and fractionation of GKRS based on cavity characteristics and evolution may improve local control while minimizing toxicity. Regular imaging follow-up is important to guide adaptive management strategies.

Conclusion

Postoperative cavity volumes after brain metastasis resection and adjuvant GKRS evolve dynamically, influenced by timing, fractionation, and target delineation. Understanding these temporal changes is crucial for optimizing radiosurgical planning and improving clinical outcomes.

References

1. Introduction references 1-13 -- Various studies on brain metastases and radiosurgery